This adds all the header ints to chunked messages, solving the problem
of losing RequestId on roundtrips if the answer was too big.
Added a unit test for this "new" features.
This makes callbacks all use shared_from_this() in order to avoid
callbacks being done on deleted instances (thanks boost!).
Last, special case when the user doesn't connect but just sends messages
which caused a send of data, only to realize the connection wasn't open,
and then a connect.
This makes sure we immediately start a connect on queue of a message.
In extreme cases we might end up going over the bounds of the internal
buffers, as such myConnection.send() may now throw.
I also cleaned up the ping design and made it a bit more strict.
Last I increased the amount of incoming data I can receive in one go,
this will make throughput higher.
TomZ