Invert Coolant, PWM & Invert Spindle Updates

I have added PWM to the Spindle, you can set the spindle as either PWM
or Stepper.

On the UNO the Y Limit switch has to be disabled to use the PWM on that
pin.
On the Mega Timer 4 has been used so it does not affect the limit switch
pins.

Status:
PWM - Tested and working
Stepper as Spindle - Tested on Scope only ( but looks good )
Invert Spindle Enable Pin - Tested on Scope
Invert Coolant Pins - Tested on Scope

A Warning has been added to pinmap.h about the invert pins will be
active for a moment while the controller is resetting.