Matcher test suite now publicly reusable

The unit tests which were in tmatch_test.go have been moved (and
rewritten for readability) into testsuite.go. It is now possible to
reuse these tests by implementing a simple interface delegating how
messages are sent and matching responses up with expectations.

The netwk package now uses this test suite to perform a complete E2E
integration test on a running system using UDP sockets.

Intending to relook at the tests inside testsuite and expand to cover
more cases. We already found one bug in the matcher during this
refactor.