Extend for Adafruit Ultimate GPS

[quietlychris]

The Adafruit Ultimate GPS also has a USB option which runs at /dev/ttyUSB0 at a baudrate of 9600. Early on, it looks like there's incompatibility with the way that the serialport reads in the NMEA strings (characters are coming in one at a time, and are not being concatenated correctly in order to form proper sentences). Given the current issue with using the the standard adafruit_gps crate, fixing this and testing against the nmea library may provide a good second option for a GPS.