Improved message decoding. ...

Now builds a dictionary of seen devices.
Monitor FFFFFF messages removed, not needed.
Catches bad payloads and prints a warning rather than crashing.
Accepts and responds to a JOIN command.
Message and value encoders written and working.
Message and value decoders written and working.

Message decoder added. ...

Messages polled at a faster rate.
Now see unsolicited switch change messages from MiHome AdapterPlus.
Removed a lot of debug messages.
Real value decoding now working.

Added source files from first working tests