Add GPIO components

[SteveDesmond-ca]

Create high-level objects for:

• RGB LED
• rotary encoder
• 7-segment display (8-pin direct)
• motor driver
• bit shift register
• timer
• LED matrix (16-pin direct)

The pins required should be passed in as parameters, and the classes should contain high-level helper methods and/or properties.

Requests for additional components should be created as their own issues.

[SteveDesmond-ca]

Some of these will probably require SPI/I2C support via #6.