Added SimplexNoise

This code adds the SimplexNoise implementation of Gustavson/Eastman. Compared to Perlin, it produces noise of similar quality at higher speeds. See [Wikipedia](http://en.wikipedia.org/wiki/Simplex_noise) for more info.

A simple micro-benchmark indicates a speed-up of one third on my machine (this is just an indicator!). The 2D and 4D implemations are a lot faster than Perlin. I think it would be nice to have this in the TS toolbox.

The Noise interfaces requires a brownian noise method (why?), and all existing classes have mostly identical implementations. I extracted the code into `BrownianNoise`, so maybe we can use this instead.