transport: added custom data and raw modes to transport/messaging layer.

transport: added custom data and raw modes to transport/messaging layer.

In addition to generic messages and the default generic message mode,
you can now put a transport into custom data and raw modes. In raw more
the transport acts as a transparent bitpipe ie. basically like a normal
socket. In custom data mode, you first describe and register the data
structures you want to pass over the transport with the messaging layer
and then you can directly pass any of these data structures to the
appropriate sending/receiving routines and the messaging layer will
automatically take care of the encoding/decoding for you.