The threading model used for processing messages here will need
redesigning; we can't allow the application to block the event loop
when processing a message in case it calls something which won't
return until a message is processed.
Final model will probably use a pool of workers which will handle I/O
one-at-a-time, blocking and allowing other threads to deal with the
I/O when in the application message callback.
The protocol is going to use TLV messages, containing zero or more
fields represented using the same TLV header. Functions for
(de)serialising DirectPlay message structures will be built on top of
these classes.
