anchor: Joystick:getGamepadMapping
  Gets the button, axis or hat that a virtual gamepad input is bound to.
  inputtype, inputindex, hatdirection = Joystick:getGamepadMapping( axis )
  axis GamepadAxis The virtual gamepad axis to get the binding for.
  inputtype JoystickInputType The type of input the virtual gamepad axis is bound to.
  inputindex number The index of the Joystick's button, axis or hat that the virtual gamepad axis is bound to.
  hatdirection JoystickHat The direction of the hat, if the virtual gamepad axis is bound to a hat. nil otherwise.
  inputtype, inputindex, hatdirection = Joystick:getGamepadMapping( button )
  button GamepadButton The virtual gamepad button to get the binding for.
  inputtype JoystickInputType The type of input the virtual gamepad button is bound to.
  inputindex number The index of the Joystick's button, axis or hat that the virtual gamepad button is bound to.
  hatdirection JoystickHat The direction of the hat, if the virtual gamepad button is bound to a hat. nil otherwise.