v0.4.0 - Speed classes, offline version

• Different speed classes can make the game much harder or easier now
• Improved AI by a LOT, should provide a real challenge now, especially on higher speed classes
• Downloadable off-line version can be played without internet connection (still requires web browser)
• Gamepad navigation for menus
• New demo/attract mode as background for the menus
• Fixed a bug where the ball would get stuck on the borders

As always, all feedback is welcome!