The 9p wire protocol

* Structure to hold requests
* Functions to serialize and deserialize requests
* Basic testing of said functions.
* TODO: strengthen parsing code (it is pretty weak right now)
Insert comment about the possibility of using the htole16 and equivalent functions in <endian.h> (or, more usefully, from https://github.com/esnet/iperf/blob/master/src/portable_endian.h)