* Add support for RetainHandling.

* Add support for No Local.

* Add support for _SubscriptionIdentifier_.

* Add more Unit Tests.

* Update docs.

This commit fixes issues which were caused by processing messages synchronously in the packet receiver loop. This blocked KeepAlive and Ack packets from being processed while a message was processed.

Fixes #648
Fixes #587
Fixes #829

- adding client and server wrappers to verify the clientid starts with the testname
- adding disposable baseclass
- clear disconnect handler from client so it does not try to reconnect after it is disposed
- moved code from dispose to cleanup in case it is called in a stop method as dispose may only be called once while start / stop may be called multiple times