Added Serial to sseg communication and GPS

The Arduino now accepts serial data with the following grammar:

S=<float>\n     //speed to write to screen 1
C=<float>\n    //current to write to screen 2

where <float> is an ascii representation of a floating pt number

GPS is also added. It spits out GPS data in NMEA sentences whenever it
gets it from the GPS module.

When the device hasn't heard anything from the PI, it sends out
Arduino_Dash