Fixed bug in Thread::incrementTickCount().

- Reworked main loop in Thread::incrementTickCount() so it works
  properly now that the lists are circularly linked.
- Fixed issue with Thread::removeFromList() when removing the only
  thread on the list. Also made it allow empty lists.
Documentation and copyright updates.
New led_ringcoder test and demo app.

- Demo app for using an LED ringcoder from SparkFun.
- Still in progress.