Blake2s Hints

[jrchatruc]

This task requires us to implement the Blake2s Hash function ourselves (as it's a custom one) and a bunch of utility functions. To do it, you can follow the Python or the Rust implementations (here and here).

Once that's implemented, the list of hints is:

• BLAKE2S_COMPUTE Implement Blake2s Hints (Part 1) #311
• BLAKE2S_FINALIZE Implement Blake2s hints (Part 2) #312
• BLAKE2S_ADD_UINT256 Implement Blake2s hints (Part 3) #314
• BLAKE2S_ADD_UINT256_BIGEND Implement Blake2s hints (Part 2) #312