Implemented a reply enumeration for the USB protocol, and a command value for the Tiva C to indicate bad command inputs
Fixed an error in the checking logic for the CMD_STOP return value in flashprog
Implemented functions to read and write the UART on the Tiva C
Implemented some global variables for use in the USB-UART communications
Implemented logic for starting a USB-UART transaction on the Tiva C
Implemented the stop portion of thee USB protocol on the Tiva C