Document paddle states

[wkeeling]

PaddleStates are used to change the behaviour and appearance of the paddle sprite. These states are transitioned to/from which can involve animation. Transitioning is not immediate, it is more a request, because an existing state may need to "animate out" before a supplied state can "animate in". As a result the state transition needs to happen in the main game loop.

This needs to be made clear in documentation. Supplying a state to the transition() method does not mean that this state will be immediately active after the transition() method completes.