Write a real client-server protocol

[Daenyth]

It should support

• User management & community aspects
• Support realtime play (a la playtak.com)
• Support async play
• Multiple rulesets at the same time (create game with explicit ruleset)
• Start a game from non-empty state

Ideally it should be

• Stateless via REST
• But optionally also able to open a websocket for live subscriptions to games/chats

Serialization format?

• Something well typed. Investigate avro, parquet, protobuf3, thrift

To do some time after #6