add a LocoMotor class

[2bndy5]

There is a use case for instantiating a single Solenoid object with 2 pins (using 2 separate solenoids in concert): an engine akin to that that of actual locomotive trains. Think about it! Each solenoid applies force in alternating turns... Of course, this requires a new Drivetrain child class that coordinates the solenoids based on a boolean-ized sensor (like a pressure switch or hall sensor) to determine when to alternate applied force between solenoids (the default behavior of the Solenoid class when its value is changed from positive to negative and vice versa).