Update some parts and add boot loader information.
Fix some board comment mistakes.
Erase non-boot portion of flash when chip erase command is received.

This works around bugs in avrdude that verify portions of flash that were
never flashed, assuming chip erase is sent (the default). However, the
boot loader will still fail verification when updated through itself
(meanwhile, avrdude is fixed in SVN).
Invert POWER_OFF to POWER_ON so that POWER_OFF does not need to be initialized.

This may also fix (or break) the MK i2c two-byte protocol, which was
relying on POWER_OFF to be set when first connecting.
Disarm after 2 seconds of signal loss.

Also beep when this occurs instead of immediately after signal loss.

This may mask some signal corruption issues and make it look like power
jitter instead, but this seems to be safer overall.
Use the LEDs on boards which have them.
Fix double-reverse (no reverse) for i2c and UART (since 934122d59).