(mqtt) WIP Test class for publisher
(mqtt) Start thinking about serialising the Reading envelope
(modbus) Publish results with UTC timestamp
(codecs) New codecs package

For binary serialization when publishing.
(modbus) Use Codec to serialise data for publication.
(mqtt) Publish raw data with data/raw path suffix
(mqtt) Specify topic root as a Topic.

Rather than a String.
(mqtt) Cleanup Publisher API

The recent cleanup of the MQTT Client API allows the Publisher API to be
simplified as it no longer requires ClientModule and the dependently
typed module.Client.  Just the Client is enough.
Merge branch 'feature-publish-results'
(modbus) Calrify the ModbusRegisterRange a little