TODO

Square offset params
backlash compensation
#112 => 2 PWM outputs: One on D8 in 0-12V and the other on another port in 0-5V, new commands such as M3.1, M4.1 and M5.1 to control the second output.
#71 => G0 should find the shortest path on Rotary Axis (wrap-around coordinate system ?)
CoreXY homing bug correction grbl-Mega-5X #124 / grbl-Mega #49
Second serial port communications
Spindle enable (laser enable) did not restore after feed hold, bug #79
Implementy analog output (PWM output) M67/M68