Added an input update check during the game loop. It checks if the input is a special command, in this case enter, and does a specific action, in this case quits the game. Later this will be used to check for commands to open menus, etc. I'm not sure about this system, though, because ideally I'd want the input update to occur exactly once per cycle, and all the rest of the systems have to use that particular character for that particular cycle. This might mean having to pass a pointer to the keyboard to the input controller, which would make the code messier.