feat(unsub-test) adds publish before unsubscribe, closes #10

- git ignores matt development message cache to
- adds a few debug log statements
- copies file path for delivery of old messages (cached on disc), so they can be cleaned up properly
- renames matt cache dir to `mqtt_cache'
- adds more complex unsubscribe test:
	- sub to topic, wait 5 seconds (for old messages to arrive)
	- pub one wait 5 seconds
	- unsub & pub another message, weit 5 seconds
	- if only 1 message arrived since the first pub the test passes.