FIELD OF INVENTION [0001] The disclosure generally relates to copolymers and copolymer compositions that are both hydrophilic and oleophobic. It further relates to membranes coated with such copolymer compositions to impart both hydrophilicity and oleophobicity to the membranes and their uses, for example, as filtration membranes for treatment of hydrocarbon-containing water. BACKGROUND [0002] Efficient removal of oily suspended solids (e.g., oil-coated dirt particles) from water is one of the major challenges in water-treatment industry. For example, large-scale methods for treatment of hydrocarbon-containing waste water (e.g., oil-containing water) in a petroleum industry may range from giant containment booms and absorbent skimmers to chemical treatments. Produced water from unconventional gas production are often disposed of by underground injection. Prior to its disposal, the produced water is treated with significant levels of biocide to prevent fouling of the disposal well. Some of these conventional water-treatment techniques have questionable effects on human health and environment. [0003] Filtration methods could provide a more efficient and scalable approach for treatment of hydrocarbon-containing water and to remove oily suspended particles. Microbial removal by microfiltration has potential to be a lower cost option than biocide treatment. However, for microfiltration to be less expensive than biocide treatment, the microfilter must be hydrophilic and not be fouled by oils present in the produced water. Ceramic membranes that are oil-tolerant have been employed for treatment of oil-containing water. However, ceramic membranes have significant disadvantages in terms of their higher weight and production costs. Further, ceramic membranes have significant limitations in application areas where oily suspended solids are to be removed from contaminated water. [0004] Polymeric membranes are suitable candidates for water treatment processes. Polymeric membranes are cheaper in comparision with their ceramic counter parts and are also more compact. The use of polymeric membranes for treating water reduces the operating cost and size of water-treatment plants employing the same. However, one of the major drawbacks of polymeric membranes is membrane fouling. Generally, membrane fouling occurs when impurities in water such as emulsified, free, or dissolved oil are irreversibly deposited on the membrane surface and/or within the internal pores of the membrane. These deposits not only decrease the membrane lifetime but also lead to a dramatic reduction in water flux, subsequently leading to an increased operating costs. Additionally, if a polymeric membrane is not hydrophilic in nature, aqueous dispersions such as oil-containing waste water cannot be readily filtered through these membranes without pre-wetting the membrane with organic solvents such as isopropanol followed by flushing with water to overcome the lack of affinity between the non-hydrophilic material and the polar aqueous dispersion. Such pre-wetting of membranes may be expensive and may also lead to "gas-lock" or "de-wetting". [0005] In view of the above, there remains a need for development of hydrophilic polymeric membranes that are both oleophobic and oil-tolerant so as to enable their use in treatment of hydrocarbon-contaminated water without being rapidly fouled by hydrocarbons. BRIEF DESCRIPTION OF THE INVENTION [0006] The invention is directed to copolymers and copolymeric compositions that are both hydrophilic and oleophobic. Membranes comprising such copolymeric compositions, which are both hydrophilic and oleophobic and/or oil-tolerant are also provided. [0007] In some embodiments, a copolymer comprising 1 to 50 mole % of a structural unit of formula I and 25 to 99 mole % of a structural unit of formula II are provided. [0008] In formulas I and/or II, R1 is a linear or branched C1-C30 fluoroalkyl group. R and R are independently at each occurrence a hydrogen, or a linear or branched C1-C4 alkyl group. In some embodiments, R4 and R5 are independently at each occurrence a linear or branched C1-C12 alkyl group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group; and R6 and R7 are independently at each occurrence a linear or branched C1-C12 alkylene group, a linear or branched C2-C12 alkenylene group, a linear or branched C2-C12 alkylnlene group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group. In some other embodiments, at least two of R4, R5, R6, or R7 together with the nitrogen atom to which they are attached may form a heterocyclic ring containing 4 5 to 7 atoms. X is independently at each occurrence either an oxygen atom (-0-) or an -NH- group; and Y is either a sulfite group or a carboxylate group. The values of m and n are independently at each occurrence an integer ranging from 1 to 5. [0009] In some embodiments, a copolymer comprising structural units derived from a mixture of ethylenically unsaturated monomers comprising 1 to 50 mole % of fluoroalkyl monomer of formula III and 25 to 99 mole % of zwitterionic monomer of formula IV is provided. [0010] In formulas II and/or IV, R1 is a linear or branched C1-C30 fluoroalkyl group. R and R are independently at each occurrence a hydrogen, or a linear or branched C1-C4 alkyl group. In some embodiments, in formula IV, R4 and R5 are independently at each occurrence a linear or branched C1-C12 alkyl group; a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group; and R6 and R7 are independently at each occurrence a linear or branched C1-C12 alkylene group, a linear or branched C2-C12 alkenylene group, a linear or branched C2-C12 alkylnlene group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group. In c some other embodiments, at least two of R4, R5, R6, or R7 of formula IV together with the nitrogen atom to which they are attached form a heterocyclic ring containing 5 to 7 atoms. X is independently at each occurrence either an oxygen atom (-0-) or an -NH- group; and Y is an anionic group. The values of m and n are independently at each occurrence an integer ranging from 1 to 5. [0011] In some embodiments, a composition comprising any of the above- disclosed copolymers is provided. In some embodiments, the copolymer comprises 1 to 50 mole % of a structural unit of formula VII, and 25 to 99 mole % of a structural unit of formula VIII, wherein R1 is a linear Cs-Cg fluoroalkyl group. [0012] In some embodiments, a membrane comprising a porous substrate and optionally a coating attached to the porous substrate is provided, wherein at least one of the porous substrate or the coating comprises any of the above-disclosed copolymers or copolymeric compositions. In some embodiments, the polymeric composition comprises a copolymer comprising 1 to 50 mole % of a structural unit of formula VI, and 25 to 99 mole % of a structural unit of formula VII, wherein R1 is a linear C5-C8 fluoroalkyl group. DRAWINGS [0013] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings. [0014] FIG. 1 shows a transmission electron microscopic (TEM) picture of z90 copolymer-coated ePTFE/PTFE membrane. [0015] FIG. 2 shows contact angles of a hydrocarbon and water on an ePTFE/PTFE membrane coated with z90 copolymer. [0016] FIG. 3 illustrates the measured flux characteristics of a z90 copolymer-coated ePTFE/PTFE membrane in comparison with an ePTFE/PTFE membrane without any copolymer coating. DETAILED DESCRIPTION [0017] The invention is directed to hydrophilic-oleophobic copolymers and membranes formed therefrom. It further relates to the uses of copolymeric compositions as coating materials on porous substrates to form filtration membranes having both hydrophilic and oleophobic properties. By incorporating both hydrophilicity and oleophobicity to a filtration membrane, such coating enables efficient filtration of hydrocarbon-contaminated water, for example, filtration of produced water to remove suspended oily particles. In absence of such coatings, hydrocarbons (e.g., as emulsified, dissolved, or free oil in produced water) may rapidly foul a filtration membrane. Oleophobicity and oil-tolerance imparted by such copolymer coating may prevent oil in the contaminated water from wetting the membrane, occluding its pores, and stopping the filtration. Further, enhanced hydrophilicity may allow passage of water through these filtration membranes without the need for prior pre-wetting the filtration membrane with solvents such as isopropanol. Thus the filtration membrane having such coatings may be effectively used for treatment of contaminated water (hydrocarbon-containing water) with less frequent cleaning requirements. Such filtration membranes also obviate the need of chemical treatment facilities, and in turn reduce the need of usage, handling and storage of environmentally harmful toxic chemicals (e.g. biocides and solvents) in field operations. [0018] To more clearly and concisely describe and point out the subject matter of the claimed invention, the following definitions are provided for specific terms, which are used in the following description and the appended claims. [0019] As used herein, the term "acyclic" refers to a compound/group which does not contain a ring. The term acyclic atom refers to an atom which is not a ring member. [0020] As used herein, the term "alicyclic" refers to a compound/group that contains non-aromatic ring(s). Alicyclic system includes polycyclic ring systems, which does not have an aromatic ring (e.g., benzene) as one of the cyclos. The term "cyclo" denotes a ring of a polycyclic ring system. As used herein the term "aromatic" refers to a compound/group having at least one aromatic ring. It also includes polycyclic ring system having at least one aromatic ring (e.g., a benzene ring) as one of the cyclos. Ring systems in general include substituted rings, including substitution in the form of additional fused or bridged ring(s). [0021] As used herein, the term "alkyl group" refers to an acyclic carbon or a saturated acyclic carbon chain represented by the formula, -CnH2n+i. [0022] As used herein, the term "alkylene group" refers an acyclic carbon or a saturated acyclic carbon chain represented by the formula, -(CnH2n)-. [0023] As used herein, the term "alkenyl group" refers to an acyclic carbon chain that contains a carbon-to-carbon double bond, and is represented by the formula, -CnH2n-i. [0024] As used herein, the term alkenylene group refers to an acyclic carbon chain that contains a carbon-to-carbon double bond, and is represented by the formula, -(CnH2n-2)-- [0025] As used herein, the term "alkynyl group" refers to an acyclic carbon chain that contains a carbon-to-carbon triple bond, and is represented by the formula, -CnH2n-3. [0026] As used herein, the term "alkylnlene group" refers to an acyclic carbon chain that contains a carbon-to-carbon triple bond, and is represented by the formula, -(CnH2n-4)-. [0027] As used herein, the term "fluoroalkyl group" refers to an alkyl group wherein at least one of the hydrogen atoms of the alkyl group is substituted by a fluorine atom. The fluoroalkyl group includes, but not limited to, a perfluorinated alkyl group, wherein all hydrogen atoms of an alkyl group are substituted with fluorine atoms. [0028] As used herein, the term "carbocyclic group" refers to chemical moieties comprising at least one carbocyclic ring. The term "carbocyclic ring" denotes a ring or ring system where all the ring members are carbons. The carbocyclic groups may be an alicyclic group (e.g., cycloalkyl groups such as cyclohexane group or cyclopentane group) or an aromatic group (e.g., a benzyl group, a benzene group, a naphthalene group or an anthracene group). The carbocyclic groups may be substituted or un-substituted. [0029] As used herein, the term "heterocyclic group" refers chemical units comprising at least one hetero ring. The term "hetero ring" denotes a ring having carbon and at least one atom from the group consisting of nitrogen, oxygen, sulfur, selenium and tellurium as ring members, and contains no other element as a ring member. To qualify as hetero ring, non-ionic bonding must exist between all ring members. Inner salt compounds such as betaines, sufobetaines etc., wherein two ring members are attached to each other by ionic bonding are not regarded as hetero rings. The heterocyclic groups/rings may be alicyclic (e.g., a piperidine group) or aromatic (e.g., a pyrrole group, a pyridine group). The heterocyclic groups/rings may be substituted (e.g., 2-methyl pyridine group) or un-substituted. [0030] As used herein, a coated membrane is referred as "oil-tolerant" if the performance of the coated membrane in an oil-containing feed is the same (or within acceptable operable limits) as the performance of an uncoated membrane in an oil-free feed stream. For example, the performance/behavior of an oil-tolerant system may not change dramatically when oil is introduced into the system. For example, with an oil-tolerant coated membrane, flux of clean water or brine may be high, but flux through an uncoated membrane may degrade rapidly when the feed contains oil. [0031] As used herein, a material with a measured contact angle of water or brine < 20° is referred to be hydrophilic, while a material with a measured contact angle of hexane or hexadecane > 60° is referred to be oleophobic. [0032] In some embodiments, a copolymer comprising structural units having formula I and formula II are provided. [0033] In formula I, R may be a linear or branched C1-C30 fluoroalkyl group and R may be a hydrogen, or a linear or branched C1-C4 alkyl group. In formula II, R may be a hydrogen, or a linear or branched C1-C4 alkyl group. Y is an anionic group. For example, Y may be a sulfite group (-SO3") or a carboxylate (-CO2") group. In formulas I and II, X may be, independently at each occurrence, an oxygen atom (-0-) or an -NH- group, and the values of m and n are, independently at each occurrence, an integer ranging from 1 to 5. In some embodiments, R4 and R5 in formula II are, independently at each occurrence, a linear or branched C1-C12 alkyl group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group; and R6 and R7 are independently at each occurrence a linear or branched C1-C12 alkylene group, a linear or branched C2-C12 alkenylene group, a linear or branched C2-C12 alkylnlene group, a C5-C12 carbocyclic group, or a C5- C12 heterocyclic group. R4, R5, R6, or R7 may be substituted or un-substituted. For example, R4, R5, R6, or R7 may be saccharide which has hydroxyl substitution. In some other embodiments, R4, R5, R6, or R7 may be such at least two of R4, R5, R6, or R7 together with the nitrogen atom to which they are attached form a heterocyclic ring containing 5 to 7 atoms. For example, in some embodiments, R4 and R5 together with the nitrogen atom to which they are attached may form an imidazole structure. The formed heterocyclic ring may be an aliphatic ring or an aromatic ring. In some embodiments, when at least two of R4, R5, R6, or R7 are connected together along with the nitrogen atom to which they are attached may generate a substituted heterocyclic ring. [0034] In some embodiments, a copolymer comprising 1 to 50 mole % of a structural unit of formula I and 25 to 99 mole % of a structural unit of formula II is provided. In some embodiments, a copolymer comprising 1 to 49 mole % of a structural unit of formula I and 25 to 99 mole % of a structural unit of formula II is provided. In some other embodiments, a copolymer is provided that comprises 1 to 30 mole % of a structural unit of formula I and 25 to 99 mole % of a structural unit of formula II. In some other embodiments, a copolymer comprising 1 to 29 mole % of a structural unit of formula I and 71 to 99 mole % of a structural unit of formula II is provided. In some other embodiments, a copolymer is provided that comprises 1 to 25 mole % of a structural unit of formula I and 75 to 99 mole % of a structural unit of formula II. In some example embodiments, a copolymer comprising 1 to 10 mole % of a structural unit of formula I and 90 to 99 mole % of a structural unit of formula II is provided. In any of the above embodiments, R1 is a linear or branched C1-C30 fluoroalkyl group; R and R are independently at each occurrence a hydrogen, or a linear or branched C1-C4 alkyl group; X is independently at each occurrence an oxygen atom (-0-) or an -NH- group; Y is a sulfite (-S03) group or a carboxylate (-C02")group. The values of m and n are independently at each occurrence an integer ranging from 1 to 5. In some embodiments, R4 and R5 are independently at each occurrence a linear or branched C1-C12 alkyl group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group; and R6 and R7 are independently at each occurrence a linear or branched C1-C12 alkylene group, a linear or branched C2-C12 alkenylene group, a linear or branched C2-C12 alkylnlene group, a C5-C12 carbocyclic group, or a C5-C12 heterocyclic group. In some other embodiments, R4, R5, R6, or R7 are such at least two of R4, R5, R6, or R7 together with the nitrogen atom to which they are attached form a heterocyclic ring containing 5 to 7 atoms. [0035] The structural units of formula I that contains the fluoroalkyl group impart oleophobicity and structural units of formula II that contains the zwitterionic group impart hydrophilicity to the copolymer. Thus the copolymer comprising the structural units of formula I and formula II is both hydrophiplic and oleophobic. [0036] The carbon backbone of the fluoroalkyl groups may be linear or branched. The fluoroalkyl groups may include cyclic structures as well. It may also include one or more heteroatoms other than fluorine (e.g., nitrogen, oxygen or sulfur atom(s)). The fluoroalkyl group may be a partially fluorinated group (e.g., -CHF2-) or a perfluorinated group (e.g., -CF3). In some embodiments, the fluoroalkyl group may be a C3-C15 fluoroalkyl group. In some other embodiments, the fluoroalkyl group may be a C