Simplify!

Inline most of the APC api, but retain inheritance from the `APC` base class.

On the way,
* figure out the details of APC mini's handshake (it sends a different identity
  request message and has no dongle challenge)
* retain the combining functionality, which appears to be a feature of the driver only
* Add the `AMBER_BLINK` color, which is what `Color(6)` happens to do, any higher clamps
  at green.  Toss on an `UNLIT` for off as well.
* PEP8 the mess a bit.
* Inline most private methods into the constructor and turn instance members into stack
  locals.