Small fixes for Python 3

Support for MIHO003 OpenSensor tested and working

Tested and tweaked for Python 3 support

Tested demos on real hardware. Works fine. ...

Observation: handling of incoming messages does not check registry,
it only checks the router, so if you don't have a device object
bound to it, it will be seen as unknown. Needs fixing, but not a high
priority.

Rationalised all comment styles. ...

The double hash (##) is reserved for commented out lines of code.
The single hash (#) is reserved for normal comments.

Moved setup code from global scope of Registry to energenie.init() ...

This makes it possible to use the registry in test cases

Energy monitor example written. ...

Not tested yet, as need to test with real devices

Standalone discovery example written. ...

Not able to test until real devices added

Iterator added to registry

setup_tool tested in simulation and works OK

setup_tool now written, ready to start testing

About half of the setup tool is written and roughly working

All registry tests now pass. ...

Requirements list reviewed.
TODO list updated for next steps

Most of Registry_test completed. ...

Just need to write code that passes the 'rx routes created' test

Moved KVS to separate module with separate test harness. ...

Will test this in isolation first before integrating with Registry

Managed to persist device configuration to registry.kvs

Beginnings of a persistent version of a class is appearing

Test harness for new Registry and KVS in place

Design of persistent registry store improved after a re-think

Pseudo code for KVS written, ready to be coded up

Factory method added to MiHomeDevice to generate a join_req for testing

Registry_test all test cases now pass for discovery

Set up test case for the final discovery test. ...

Test not run yet, and code is missing, marked with ####HERE####

Join_ack working on discovery mode autojoin

Auto discovery tested and working with accept

Initial outer testing of 4 discovery modes done ok

Framework of discovery methods in place, ready to TDD

Design for discovery agents done

Default incoming message callback added to router, for logging/debug

Router unknown message handling callback registration is cleaner