Methods in this protocol

A screen object provides the basic lifecycle for a game. Simple games may only need to have one screen. They are a useful way to isolate different aspects of your game. For example, you could make one screen display the title and menu, and another screen contain the game itself. You can create a screen by using `reify` like this: ``` (def main-screen (reify p/Screen (on-show [this]) (on-hide [this]) (on-render [this]))) ```