Consolidate encoder modules

[alexeden]

Removes the QuadEncoderModule, which was added to support Adafruit's quad rotary encoder device, in favor of updating (with breaking API changes) the existing EncoderModule to support both single and multiple encoder devices. This is more in line with the underlying seesaw firmware and Adafruit's C++ and Python driver libraries.

The module's methods now require that you specify which encoder you're referring to. In the case of a single encoder device, the value is always 0.

e.g.

// previously
let position = encoder.position().expect("Failed to get position");
// now
let position = encoder.position(0).expect("Failed to get position");