of: remove redundant cstruct definitions
of: all xid types refer to OpenFlow_Header.xid

Directly or indirectly, now all xid types in every module is a synonym
for OpenFlow_Header.xid.
of: constants for common protocol message types

OF0x01 and OF0x04 share many common message types. Define some of these,
in particular the ones that are necessary for a minimal handshake.
async: Add local to Platform.Trans

This is equivalent to the local function in a reader monad. Transform
the read value for some sub-computation.
async: Add allocating marshal' to Message interface

marshal' is just like marshal except it performs the necessary
allocation. Its return type is also the Chunk type, which is at times
convenient.
async: Chunk Controller (w/ handshake) implementation
async: rewrite 0x01 controller in terms of chunk controller
async: OpenFlow0x04 controller