TECHNICAL FIELD [0001] The present invention relates to a filter capable of adsorbing components dissolved in liquids. BACKGROUND ART [0002] A filter including stacked layers of a fibrous adsorbent has been proposed as a means for adsorptively removing components dissolved in liquids. [0003] Patent Document 1 discloses a filter medium obtained by processing ion-exchange fibers for removing ions in water into nonwoven fabric, followed by stacking. [0004] Patent Document 2 discloses knitted fabric of fibrous activated carbon for removing impurities in liquids. [0005] Patent Document 3 discloses a filter obtained by forming a fibrous adsorbent for removing Na ions or the like in water into woven or knitted fabric and winding the fabric around a perforated core. CITATION LIST PATENT LITERATURE [0006] Patent Document 1: JP-A-S62-68509 Patent Document 2: JP-A-2002-235247 Patent Document 3: JP-A-2012-040526 SUMMARY OF INVENTION TECHNICAL PROBLEM The woven or knitted fabric of a fibrous adsorbent described above has a certain degree of adsorbing ability, but fiber diameter or size of interstices is not controlled. Although the rate of adsorption may be heightened by reducing the fiber diameter and a prolongation of filtration life with a limited packing space may be attained by heightening the degree of packing with the adsorbent, all these measures increase the water-passing resistance during liquid filtration. It is hence impossible with prior-art technique to attain all of high adsorption rate, prolonged filtration life, and low water-passing resistance. [0008] An object of the present invention is to provide a filter having reduced water-passing resistance, a high removal ratio, and a long filtration life. SOLUTION TO PROBLEM [0009] The filter of the present invention for attaining the above object is as below. (1) A filter including at least one of a stacked woven fabric, stacked knitted fabric and a wound fiber body, the woven fabric, the knitted fabric and the wound fiber body satisfying the following requirements (a) and (b): (a) containing a fiber capable of adsorbing a component dissolved in a liquid; and (b) the fiber having a diameter D of 100 urn or more and 600 um or less, and the filter satisfying the following requirements (c) and (d): (c) having a porosity of 15% or more and 70% or less; and (d) having a variation in an areal porosity of 15% or less, in a stack thickness direction in a case when the filter includes the woven fabric or knitted fabric, or in a radial direction in a case when the filter includes the wound fiber body. (2) A filter for liquid filtration, including at least one of a stacked woven fabric, stacked knitted fabric and a wound fiber body, the woven fabric, the knitted fabric and the wound fiber body satisfying the following requirements (a) and (b): (a) containing a fiber capable of adsorbing a component dissolved in a liquid; and (b) the fiber having a diameter D of 100 um or more and 600 um or less, and the filter satisfying the following requirements (c) and (d): (c) having a porosity of 15% or more and 70% or less; and (d) having a variation in an areal porosity of 15% or less in a direction along which the liquid is filtered. (3) The filter according to the above (1) or (2), in which the woven fabric or knitted fabric has a basis weight of 300 g/m2 or more and 1,500 g/m2 or less. (4) The filter according to any one of the above (1) to (3), including a woven fabric that satisfies the above (a) to (c) and satisfies the following expression: 0.5 Woven or knitted fabric or yarns were immersed in RO water (reverse-osmosis filtrate water) for 24 hours and then examined with a microscope to measure the diameters of ten fibers. An average of these was taken as the fiber diameter (yarn diameter). In the case where the woven or knitted fabric was one configured of bundles of a plurality of filaments, the diameters of the fiber bundles were measured. In the case of woven fabric, the gap between warps and the gap between wefts were measured with a microscope at ten portions each, and an average of the measured values was taken as the opening size of the fibers. [0082] Woven or knitted fabric or a wound body was loosened to obtain yarns. In water, the yarns were packed into a column with a diameter of 40 mm and a height of 20 mm (capacity Vt = 25.12 cm3) up to the brim of the column without applying any load to the yarns, and the column was closed. This column was taken out of the water, and the water adherent to the outer surfaces of the column was wiped off. Thereafter, the column was opened, and the total mass Wt (g) of the water and yarns inside was measured. Subsequently, the water adherent to the yarns was removed by suction filtration, and the mass Wa (g) of the wet-state yarns was measured. The value of [Wt (g)]~[Waa (g)], that is, the mass Ww (g) of the water which had been present in the interstices of the packed layer, was calculated. [0083] The density pa of the fibers was calculated using the following equation. pa=Wa/(Vt-Vw) (1) Wa (g): mass of wet-state fibers Vt (cm3): capacity of vessel for measurement Vw (cm3): volume of water present in the vessel for measurement [0084] The porosity s (%) of a filter was calculated with the following equation. s (%) = (Vf-Wb/pa)/Vfx 100 (2) Vf (cm3): volume of packed (stacked or wound) fiber layer; namely, sum of the volume of packed fibers and the volume of spaces among the fibers Wb/pa (cm3): volume of the fibers (Vf-Wb/p) (cm3): volume of interstices Wb (g): mass of the wet-state fibers included in the filter pa (g/cm3): density of the wet-state fibers [0085] In the Examples and Comparative Examples, in cases when a column having a diameter of 40 mm and a thickness of 20 mm was used, the volume Vf was 25.12 cm3. In the case of a cylindrical wound fiber body including a core disposed inside, the volume Vf was calculated by subtracting the volume of the core from the volume {(R/2)2x7rxH} calculated from the outer diameter R and height H of the wound body. [0086] A filter was immersed in water, and air was then passed therethrough to remove the water present in the interstices among the fibers of the packed layer. Next, the packed layer was examined by X-ray CT scanning to obtain two-dimensional images perpendicular to the thickness direction of the packed layer. The resolution (m/pixel) was set at 1/20 the fiber diameter D, and the size of the examined field of view was set at 512 (pixels) x 512 (pixels). The packed layer was scanned while shifting the position from the center of the thickness thereof at intervals equal to the resolution of the two-dimensional images to obtain 256 images along each of the backward and forward directions, thereby obtaining 512 images in total. In the case where the thickness is less than 512 (pixels), only the images of portions where the fibers had been present were used for calculating the variation. [0087] The two-dimensional images obtained were each binarized, and the areal proportion (%) of void regions to the whole area of each image was defined as areal porosity. The areal porosity was plotted along the thickness direction and an approximate straight line was calculated by the least square method. Next, with respect to each position, the value on the approximate straight line of areal porosity was subtracted from the measured value of areal porosity, thereby determining a deviation in areal porosity at the position from the approximate straight line. The variation in areal porosity was defined as the difference between the maximum deviation and minimum deviation from the approximate straight line of areal porosity measured along the thickness direction. [0088] An aqueous solution having a calcium chloride concentration of 2 mmol/L and a sodium hydrogen carbonate concentration of 2 mmol/L was used as raw water to measure a calcium-ion removal ratio. The raw water was passed through the filter at a space velocity SVof500(hr_1). The permeate was sampled in an amount of 10 mL every time when the raw water had passed through the filter in an amount of 10 bed vol., and the calcium ion concentration in the permeate was determined by ICP-AES (inductively coupled plasma-atomic emission spectrometry) to calculate the calcium-ion removal ratio, "bed vol." is a value obtained by dividing the volume of the permeate by the volume of the packed layer. The calcium-ion removal ratio determined after the raw water had passed in an amount of 10 bed vol. was taken as "initial removal ratio", and the value of bed vol. which was obtained when the calcium-ion removal ratio had become 50% was taken as "filtration ability". [0089] 5 Pure water was passed through a filter to determine the pressure loss, which was the difference between the filter inlet pressure and the filter outlet pressure. A value "A" (Pa/m) obtained by dividing the pressure loss by the thickness of the packed layer was determined while changing the permeate flow rate (m/s). Next, water was passed through the device 0 containing no sample charged therein, and a value "B" obtained by dividing the resultant pressure loss by the thickness of the packed layer was determined while changing the permeate flow rate. The value B was subtracted from the value A, and a relationship between a value obtained by dividing the pressure loss of the sample by the thickness of the packed layer and the flow rate was plotted. Thus, a directly proportional relationship was 5 ascertained. From the inclination of this straight line, the water-passing resistance (Pa-s/m2) of the sample in the packed layer was determined. [0090] (Reference Example 1: impartation of ion-exchange ability to woven or knitted 0 fabric) About 10 g of woven or knitted fabric configured of PET fibers was immersed in 1 L of an aqueous solution containing 33% by mass poly(acrylic acid) 25,000 (manufactured by Wako Pure Chemical Industries, Ltd.) and 15% by mass polyglycerol polyglycidyl ether (EX-512, manufactured by Nagase ChemteX Corp.). Subsequently, this fabric was treated with a 5 mangle to remove the solution therefrom and heated at 130°C for 3 minutes. The resultant woven or knitted fabric was rinsed with running water and dried by reheating at 130°C for 3 minutes. The immersion of the woven or knitted fabric in the solution, solution removal, heating, rinsing, and drying were taken as one cycle, and three cycles were performed. The ion-exchange-fiber woven or knitted fabric obtained was immersed for 1 hour in a 0.1 mol/L 0 aqueous solution of sodium hydroxide to convert the carboxy groups into the sodium form. Furthermore, this fabric was rinsed with RO water until the rinse water came to have a pH of 8 or less. [0091] (Reference Example 2) About 10 g of PET fibers were immersed in 1 L of an aqueous solution having the same composition as in Reference Example 1, which contained the poly(acrylic acid) and the polyglycerol polyglycidyl ether. Subsequently, the fibers were treated with a nozzle having a diameter of 430 um to remove the solution therefrom and heated at 130°C for 3 minutes. The resultant fibers were rinsed with running water and dried by reheating at 130°C for 3 minutes. The immersion of the fibers in the solution, solution removal, heating, rinsing, and drying were taken as one cycle, and three cycles were performed. The fibers were wound around a perforated core. The thus-obtained wound body of the ion-exchange fibers was immersed for 1 hour in a 0.1 mol/L aqueous solution of sodium hydroxide to convert the carboxy groups into the sodium form. Furthermore, the wound body was rinsed with RO water until the rinse water came to have a pH of 8 or less. [0092] (Example 1) Using 84-dtex 72-filament PET fibers, knitted fabric was produced with a 22-gauge circular knitting machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce knitted fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. Sheets of the knitted fabric obtained were stacked in a column having a diameter of 40 mm and a thickness of 20 mm, the number of the sheets being two times that in Comparative Example 1, which will be given later, and this column was closed. The performances are shown in Table 1. [0093] (Example 2) Using 215-um 40-filament PET fibers, woven fabric in which the number of meshes was 42 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0094] Using 318-um 40-filament PET fibers, woven fabric in which the number of meshes was 17 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0095] (Example 4) Using 60-um 40-filament PET fibers, woven fabric in which the number of meshes was 80 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0096] (Example 5) Using 90-um 40-filament PET fibers, woven fabric in which the number of meshes was 94 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0097] (Example 6) Ion-exchange ability was imparted to 215-um 40-filament PET fibers by the method described in Reference Example 2 to produce ion-exchange fibers having the fiber diameter shown in Table 1. Subsequently, the ion-exchange fibers were wound around a perforated core with an outer diameter of 42 mm under the conditions of a traverse width of 110 mm, a traverse speed of 8 mm/s, and a spindle rotational speed of 105 rpm, thereby producing a wound body having an outer diameter of 62 mm and a height of 110 mm. The performances are shown in Table 1. [0098] (Comparative Example 1) Using 84-dtex 72-filament PET fibers, knitted fabric was produced with a 22-gauge circular knitting machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0099] (Comparative Example 2) Using 318-um 40-filament PET fibers, woven fabric in which the number of meshes was 10 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0100] (Comparative Example 3) Using 60-um 40-filament PET fibers, woven fabric in which the number of meshes was 49 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. (Comparative Example 4) Using 20-um 40-filament PET fibers, woven fabric in which the number of meshes was 420 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0102] (Comparative Example 5) Using 20-um 40-filament PET fibers, woven fabric in which the number of meshes was 230 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0103] (Comparative Example 6) Using 500-um 40-filament PET fibers, woven fabric in which the number of meshes was 18 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0104] (Comparative Example 7) Using 500-um 40-filament PET fibers, woven fabric in which the number of meshes was 14 (per inch) for each of warp and weft was produced with a plain-weaving machine. Ion-exchange ability was imparted to the woven fabric by the method described in Reference Example 1 to produce woven fabric configured of ion-exchange fibers having the fiber diameter shown in Table 1. In water, sheets of the thus-obtained woven fabric configured of the ion-exchange fibers were stacked in a column with a diameter of 40 mm and a thickness of 20 mm up to the brim of the column without imposing any load on the sheets, and this column was closed. The performances are shown in Table 1. [0105] (Comparative Example 8) Ion-exchange ability was imparted to 215-um 40-filament PET fibers by the method described in Reference Example 2 to produce ion-exchange fibers having the fiber diameter shown in Table 1. Subsequently, the ion-exchange fibers were wound around a perforated core with an outer diameter of 42 mm and a length of 110 mm under the conditions of a traverse speed of 8 mm/s and a spindle rotational speed of 104 rpm, so as to result in the same shape as in Example 6. The performances are shown in Table 1. [0106] As Table 1 shows, Examples 1 to 6 were superior to Comparative Examples 1 to 8 in initial removal ratio, filtration ability, and water-passing resistance although the same fibers were used. It is thought that the higher the filtration ability, the longer the life. [0107] While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application filed on February 28, 2017 (Application No. 2017-036090), the entire contents thereof being incorporated herein by reference. A inter comprising at least one ot a stacked woven tabnc, stacked knitted tabnc and a wound fiber body, the woven fabric, the knitted fabric and the wound fiber body satisfying the following requirements (a) and (b): (a) comprising a fiber capable of adsorbing a component dissolved in a liquid; and (b) the fiber having a diameter D of 100 um or more and 600 um or less, and the filter satisfying the following requirements (c) and (d): (c) having a porosity of 15% or more and 70% or less; and (d) having a variation in an areal porosity of 15% or less, in a stack thickness direction in a case when the filter comprises the woven fabric or knitted fabric, or in a radial direction in a case when the filter comprises the wound fiber body. [Claim 2] A filter for liquid filtration, comprising at least one of a stacked woven fabric, stacked knitted fabric and a wound fiber body, the woven fabric, the knitted fabric and the wound fiber body satisfying the following requirements (a) and (b): (a) comprising a fiber capable of adsorbing a component dissolved in a liquid; and (b) the fiber having a diameter D of 100 um or more and 600 um or less, and the filter satisfying the following requirements (c) and (d): (c) having a porosity of 15% or more and 70% or less; and (d) having a variation in an areal porosity of 15% or less in a direction along which the liquid is filtered. [Claim 3] The filter according to claim 1 or 2, wherein the woven fabric or knitted fabric has a basis weight of 300 g/m2 or more and 1,500 g/m2 or less. [Claim 4] The filter according to any one of claims 1 to 3, comprising a woven fabric that satisfies the above (a) to (c) and satisfies the following expression: 0.5