Add binary protocol deserialization code; make stuff more thread-safe

- We can now deserialize binary protocol messages! Yay!
  - However, we still need to get some protobuf stuff going to decode the actual
    user messages, because of course we do.
  - Also our dependencies increased, although probably not because the extra
    stuff might have been in our dependency tree anyways.
- You could try and do connection stuff on the main thread and data-race with
  the websocket handling thread. Now, that's somewhat less likely.
  - We actually take a lock when doing things.
  - The hope is that user code will either use our lock-taking functions, or
    take the lock themselves.
    - We probably need to write user-facing accessors that check the lock has
      been taken before doing their thing.