Adding the makefile options ADB_MOUSE_ENABLE and ADB_MOUSE_ACCMAX.
Might have gone overboard with comments, and tried but failed at not
adding more than necessary outside the converter/adb_usb/ folder.

https://github.com/dastels/tmk_keyboard/tree/master/converter/sun3_usb

- change protocol stack to LUFA

 * can be enabled by defining Makefile macro SERIAL_MOUSE_MICROSOFT_ENABLE or
   SERIAL_MOUSE_MOUSESYSTEMS_ENABLE.
 * Serial implementation can be chosen via SERIAL_MOUSE_USE_SOFT and
   SERIAL_MOUSE_USE_UART macros
 * UART configuration still has to be done in config.h: I added working clauses
   for both mouse protocols to ps2_usb's config.h

When using the PS/2 interrupt implementation, the DATA pin should be
PD0 as the documentation (README.md) states.