Use built-in HIDAPI device filtering.
Add way to open device with highest interface number.
Make getEmotivDevices return devices in order of interface number
Reduced some bonkers indent levels.
Big state refactoring. Also 100% haddock coverage.

We now have
  * EmotivPacket
  * EmotivState
to make a difference between incremental packets state we maintain.
Export all functions, add haddock sections