In addition to adding unit tests for the "Hello" message,
the following notable improvements are included:
* Separate websocket callbacks from the hub via a handler API
and adaptor.
* Move all application specific state to the session.
* Session no longer refers to the hub.
* Remove redundant MessageRequest struct.
* Hub is no longer responsible for buffer pool or
buddy image management.
* Consolidated connection table locking in the hub.
* Remove redundant session table from the hub.
* Split room join and leave into separate handlers.
This also removes the RoomConnectionUpdate struct.
* Entirely remove room management from the hub.
This also provides room operations with a separate mutex.
* Split stats into a separate service.
* Simplify the session token handler.
* Buddy image HTTP handler no longer takes the entire hub.
* Centralize JSON encoding and decoding. This removes JSON
encoding from the room worker queue.
* Improve unicast message statistics.
* Numerous other renamings and cleanup items.
Lance Cooper