Sanguino3G Firmware v1.2

Changes from v1.1:
* Introduction of circular buffer cursors, allowing us to easily abort
  processing of a command.
* Reduced blocking waits, reducing the chance of build burps.
* Added support for storing per-machine configuration data in the EEPROM.
* Support for inverting individual axes via EEPROM configuration bits.
* Better support for aborting and pausing builds.
* Stops extruder on abort.