Added basic HUD, ENUM for GameState, fling ball.

Basic HUD shows lives left plus score. GameState keeps track of the game
state, e.g., pregame and playing. PreGame allows the player to fling the
ball in any direction. When the ball hits the bottom, life is lost.
Gotta work on some brick-ball collision, and also velocity change on
ball-paddle collision, depending on how fast paddle is moved.