Module Pattern

Use the module pattern
(http://www.adequatelygood.com/JavaScript-Module-Pattern-In-Depth.html)
for the game object.  This is to better ecapsulate private members.
Input

Add an event listener on the game object to receive and eventually
forward the events to the current game state.
Screen

-Screen objects have a render function and a handleInput function.
-Create a module that contains our game's screens.  The first one we
have is the startScreen.
-The game keeps track of the current screen and any rendering and input
is forwarded along to the screen.
-Create the start screen on creation of the game.