Installs the joystick handler.
Returns true if the joystick is up.
Returns true if the joystick is down.
Returns true if the joystick is left.
Returns true if the joystick is right.
Returns true if the joystick's button 1 is depressed.
Returns true if the joystick's button 2 is depressed.
Call this regularly to update the joystick values.