Encoder code

[DepthDeluxe]

Need code inside Encoder class that will allow us to read data from a quadrature encoder. Not sure if we want to use a quadrature decoder yet.

[DepthDeluxe]

according to Phil, Avago makes good quadrature decoders. The link to the first one that comes up in Google is below

http://www.avagotech.com/pages/en/motion_control_encoder_products/integrated_circuits/decoder_ic/hctl-2032-sc/

[DepthDeluxe]

note: Grant, Mustafa, and Laura have implemented a Quadrature decoder in the FPGA, may be using that so we don't have to get hardware.