Major improvements:
-deals with joystick automatic reconnection
-deals with serial link automatic reconnection

Minor improvements:
-suppress useless pygame display
-better fit the NMEA standard with carriage return and line feed
-change baudrate to 57600

Change interface of message sent. They are now between -127 and 127 (-1 to 1 previously)
This sketch decode nmea messages on serial port and send orders to sabertooth card controlling motors.