AutoPong sample added

[MrGrak]

Hi! I'd like to add a sample game to this repo. It's a simple example of pong that plays itself called AutoPong. I think it offers a very simple introduction to game design and managing game state, perfect for beginners to take apart and play with. It also shows a very simple way to get soundfx playing in a game. The game has some unique properties, for example no content is loaded from hard drive. Instead, the graphics, soundfx and musical jingle is created using only code. It's also relatively small, at around 330 lines total. This should work cross platform, assuming that SpriteBatch + DynamicSoundEffectInstance have been implemented on that platform. Cheers

[SimonDarksideJ]

Thanks for the sample @MrGrak , it has been incorporated in to the 3.8.1 sample set, which is now live