Top level source directory. Each subdirectory contains specific code
which supports the indicated transport mechanism.  The common subdirectory
contains modules which are transport mechanism agnostic.

Each sub directory should contain the following directories:
	src 	- Actual C source modules
	include - Header files
	test 	- Unit test code and scripts to drive when necessary

Also at this level in the file tree, a test directory contains code
which supports all of the specific unit test code in each of the other
three directories.