Chain server pt2

[arthurpaulino]

This is a sequel to #1173

• Add better documentation to the server, both on the README and in the chain-server crate files (using #![deny(missing_docs)])
• Add the new chain_acc and compress endpoints, which only work in stream mode

• chain_acc does the folding internally as a checkpoint, but does not perform compression and does not return a proof
• compress finally compresses the accumulated recursive SNARK and returns it