[After TMM] Revise protocol documentation

We really need a dedicated server protocol document where we write down what messages are sent by the client, and what responses come from the server. That way the client developers can have something to reference without needing to read the server code. This would also push us toward defined protocol versions where we can explicitly say "version 1.0 has exactly these commands".

Ideally we would refactor the server so that much of this documentation could be generated automatically from doc strings.