Removed synchronize mode.
Decrease usbserial timeout to one second, drain usbserial buffers on receive error.
Cleanup, renamed variable, documented code.
Speedup reset().
Cleanup, removed unused stuff.
Added 'errorFlags' variabe to log usbserial errors for debug
(ExtendedStats).
Added display of 'errorFlags' variable into ExtendedStats menu to display
usbserial errors for debugging reasons.
Code documentation, better errorhandling.
* Set errorFlags on usbserial errors.
* split common code out of get_coordinates() and
  get_coordinates_packed() into doAutoretract().
* Disabled G2 (CW ARC) and G3 (CCW ARC) to save program memory.