Smarter number-printing functions.

Manually print numbers in decimal using the new functions.  Temporarily
added to the MAX7345 class although that's not the right place for it.
Replace a few printf's with simple write() calls.

Whoever thought it was a good idea to use printf on a tiny atmega chip?
Use higher-res horizonal line chars.
Update the font file again.
Fix a few type-mismatch compiler warnings.
Rewrite warnings panel, add Mag & Accel warnings.

Greatly simplified.
Pass 16-bit angles for pitch&roll in the simple proto.
Use the new chars to show altitude in ILS.
Don't show home direction if home position not set.
Fix the rose central direction calculation.
Simplify the home arrow direction calculation.
Set a valid default home direction value.
Make sure home alt doesn't get set without any data.
Better take-off time decision, motor must be armed.