Da encoding protocol

[danielSanchezQ]

• Fill up the encoding protocol structure with the actual specification
• Expand an implement tests

[megonen]

We can use SHA3 (Keccak) for hash. (since it's a newer standard). It is called sha3_256() in hashlib.

[megonen]

I have a new idea. We can publish column commitments, but when calculating the agg_com value, we can calculate the commitment value of H(ColumnComm)_i values. This way, if someone wants to add an extra column, they will not be able to add it because it is over the agg_com hash, and we will provide the things we provided in our previous design.

[megonen]

LGTM