Changed RQ_DIGITAL_WRITE command to RQ_PIN_VALUE. For now is just a rename but eventually (when pwm is added) it will decide whether to simply make a digital write or activate a pwm on the given pin. Also, fixed a bug when writing a pin: instead of using PORT I'm using LAT register now.
Smalltalk commit.

* Lots of changes. Starting to implement a proper object model to represent different devices. Added attaching and configuring mechanisms. And implemented a few basic devices: LED, Potentiometer, Servo, and ContinuousServo.