oft: improve help text
update documentation

Developer-only documentation was moved to DEVELOPING. Redundant usage
information was removed from oft.
move and check in OpenFlow protocol modules

Move all the protocol code out of the oftest package and into a of10 package to
prepare for supporting more OpenFlow versions.

The generated code is now checked-in to make it simpler to use OFTest.

Backwards compatibility with out of tree tests is maintained by aliasing the
old module names. The basic test module has been changed to use the new API.
copy in of11 package

These modules were copied from the oft-1.1 branch.
oft: support prefixing test names with ^ to remove them from the test set