- Implemented USE_SPINDLE_SERVO_MODE configuration option
- Changed Timer2 prescaler from 1/8 to 1/1024 for ~50Hz servo frequency
- Added configurable servo pulse width range (SPINDLE_SERVO_MIN_PULSE/MAX_PULSE)
- M3 S0-S1000 now controls servo position (0-180 degrees)
- M5 positions servo to maximum position (pen up) instead of disabling PWM
- Default configuration supports pen plotter with reversed pulse values (MIN=31, MAX=16)
- Only supports ATmega328p (Arduino Uno) processors
Based on: https://www.buildlog.net/blog/2017/08/using-grbls-spindle-pwm-to-control-a-servo/
