Add GPIO components

[SteveDesmond-ca]

Create high-level objects for:

• [x] RGB LED
• [x] rotary encoder
• [x] 7-segment display (8-pin direct)
• [x] motor driver
• [x] bit shift register
• [ ] timer
• [x] 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.