Function:    JoyX()

           This function will return the current X position of the stick.
           When positioned at the complete left, this should return 0 or
           values close to that, at the right it should return some maximum
           value (depending on the speed of the machine), and in the middle
           it should return about half of right's value. Your program should
           thus first initialise some machine dependant values. Once
           understood how it works, it is easy to figure out the rest.

  Syntax:      JoyX([nJoyNr]) --> nX

  Arguments:   JoyStick #1 if none is supplied, otherwise 0 indicates #1,
               1 indicates joystick #2.

  Returns:     A numerical, generally between 0 and . 255, machine
               dependant.

  Usage:       * Assuming JoyMiddle is some initialised variable ..
               if JoyX() < JoyMiddleX
                    MoveRight()
               endif