feat(mqtt) Anonymous-Announcement boilerplate code

Closes #23
Merge pull request #27 from vsaw/23-mqtt-subscribe-anonymously

feat(mqtt) Anonymous-Announcement boilerplate code
feat(mulicast-channel-init) creates and announces channel when subscription is found

- adds DLL of multicast channel (new struct)
- checks if channel of topic exists
- checks if the matching channel (if any) has been announced for this accept state or if the announcement is still active (via expiration)
- creates new channel if necessary
- (re-)announces channel
chore(makefile-add-multicast) adds multicast to linker flags
chore(logging) define handy logging stuff
fix(channel-announcement) improves channel announcement upon subscription discovery
feature(multicast-publish) adds multicast channel creation and publish upon MQTT_publish
fix(channel-init) finalize channel initialization and publish closes #22