Add 2D open simplex noise.
Factor the gradients out into a common file, because Perlin and Simplex noise use the same ones.
Update README.md for addition of 2D simplex noise.
Simplex example no longer lists files that aren't generated.
Add a simple test for 2D simplex noise.
Fix the simplex test by making it so we can inject a Rng into Seed, and using XorShiftRng. Also change Seed to use XorShiftRng by default.
Remove the Simplex test. Will replace with image tests later.
Merge pull request #34 from Cifram/master

Add 2D OpenSimplex noise.