TODO
 
- Implement an event system.

- Simplify the api. Input and output reports should be consistent, now they
  are split in wiimote_event.h and wiimote_report.h.

- Improve support for the built-in speaker.  

- Support the classic controller, currently it is assumed that the nunchuk
  is the only device that will be plugged in to the extension port.

- Add configuration options.