code: def speed_heading(msg):
      
      spd, trk_or_hdg, rocd, tag = velocity(msg)
      return spd, trk_or_hdg
docs: Get speed and ground track (or heading) from the velocity message
      (handles both airborne or surface message)
  
      Args:
          msg (string): 28 bytes hexadecimal message string
  
      Returns:
          (int, float): speed (kt), ground track or heading (degree)