Lightweight library for the Arduino CNC Shield
(https://blog.protoneer.co.nz/arduino-cnc-shield)

A lightweight library for the Arduino CNC Shield wich allows you to control each motor individually, without the need to configure GRBL.

How to use it:
    1. Create the *CNCShield* object.
    2. Call the *CNCSHield.begin()* method in the setup step.
    3. Enable the shield by calling *CNCSHield.enable()*
    4. Get a *StepperMotor* object using *CNCSHield.get_motor()*.
        - motor_id 0 -> X axis
        - motor_id 1 -> Y axis
        - motor_id 2 -> Z axis
        - (for now only X, Y and Z axis work)
    5. Set the direction (*CLOCKWISE* or *COUNTER*) of the *StepperMotor* using *StepperMotor.set_dir()*.
    6. Call *StepperMotor.step()* every time you want your stepper motor to make a step.
    * for a working examples see examples.