Initial implementation of the MIDI tuning standard

Preliminary implementation of MTS.

- Only receives MTS bulk tuning messages.
- Tunings are not saved at this time.
- Impact on "untuned" mode (equal tempered) is mainly an extra 256-bytes to store the tuning. Also takes an extra 32-bit divide operation in tuner_computeCVFromNote(), but this would be easy to optimize out later.

Minor changes to DEBUG:
- Slightly more granular/modular "#define DEBUG"
- Configure stdio (stdout, printf, etc) when DEBUG is defined. Printf makes it much easier to format complex debug information. Only adds 200 bytes to the debug firmware image.