deadband ready for testing
deadband compensation added to the gw::Motor

  - new private function deadband_compensate() takes the
    raw pwm signal and compensates for deadband in the motor.
  - set_deadband(int forward, int reverse) allows gw::Motor
    users to set deadband in the range [0, 255] and [-255,0]
    respectively for each motor direction.
  - use a script similar to the example in Glow_worm/examples
    called deadband_solver.ino to find the deadband for each
    motor once it is mounted in the robot.