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/)


not sure, but maybe you could drop the now from above if it gets initialized at the start of the animate block either way :)