Tsne

This is a Torch implementation of t-SNE, a wrapper to Barnes-Hut t-SNE, and a demo with both implementation for visualizing MNIST digits (requires 'mnist' and 'gfx.so'). Both implementations also rely on 'unsup'.

As this is my first ever Torch commit :-), please check carefully whether I didn't introduce anything inconsistent with the rest of the repo, and whether I did the .rockspec file correctly.

Below a screenshot of the output produced by the demo (t-SNE left, BH t-SNE right).

![screen shot 2014-07-25 at 14 35 51](https://cloud.githubusercontent.com/assets/1168046/3702229/c310f658-13fc-11e4-8d75-29a43c376054.png)