This implements a ringbuffer that is used to decouple the raw websocket
connection from the messages that the game handler handles.
There is still a problem:
Test_MessageBuffer_GetWaitsForNewDataIfOldOneWasAlreadyGotten fails
because buf.Get() returns an old value instead of waiting for a new one.
This must be fixed.
Additionally, the Insert() and Get() methods must be thread-safe at
some point. But since Get() blocks when there is no data, there would be
a deadlock if I see this right.
