This should resolve any cases where sessions were not removed from the hub
after their connection closed.
Also moves buddy image management entirely into the session and
vastly improves locking around session data. Also allocates less
when sending client left messages and paves the way for session specific
message codecs.
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.
Simon Eisenmann
Lance Cooper