===========
TODO items:
===========

0. Fix the errant VOX trigger when the sketch first starts (USB first powered).
1. Add configuration blocks to the keying types, removing the global #defines.
2. Add documentation describing the pins that can be used for GPIO, and the
   pins that are reserved for the audio device shield.
3. Allow more than one keying object to be attached to each audio channel.
4. Allow more items to be configured via serial device and persisted to EEPROM.
