added a basic tetris game to the samples

I added a basic Tetris game to the samples, it's a (partial) port of an old javascript version. I thought it would be an easy way for me to start making a simple contribution (I'll tackle some real issues when I have a little time)

FYI: there is a brief blog post [here](http://codeincomplete.com/posts/2014/11/7/tetris_shoes/)


You already have a lot of constants up there (which is great) - might be worth adding the 100 and the 2 there with descriptive names :)