In game menus.

Single player games:
 * Pauses the game.
 * Allows restarting the game, selecting another game, or returning to the main menu.

Multiplayer games:
 * Doesn't pause the game (for obvious reasons).
 * Allows leaving the game more gracefully than before.

Thanks to those who recommended this via GitHub. Please feel free to contribute any other ideas to make this game as good as can be.
