bumped curv-kzen to 0.10 + Upgraded code to compile

[gdnathan]

Bumped curv-kzen to 0.10.

Notable changes to files:

• Now that VerifiableSS takes a second generic parameter H: Digest + Clone, I used sha2::Sha256 as this generic parameter, as the curv-kzen lib does
• VerifiableSS also takes a new "proof" field. As there is no default, I copied the logic from one of the files of curv-kzen and did this:

    let witness = Scalar::random();
    let proof = DLogProof::<Secp256k1, Sha256>::prove(&witness);

• As Sha256 implement neither Serialize nor Deserialize, some of the tests doesn't pass anymore. I commented them out until we find a solution. If you have any required change, or any advice on how to fix the deserialize/serialize issue, please tell me.