4 Axes version for boards with i2c stepper current chip

• Boards with I2C stepper current chip (like Smoothieboard, MKS SBASE) needs to set current with $140..143.
• PWM out on pin 2.5
• Additional setting $33 for PWM frequency (default 5000Hz)
• Default settings are for K40 (40W chinese laser engraver)
• Set $5=0 if you have optical endstopps (normaly open)