Add SimplexNoise and NoiseTexture as new resources

SimplexNoise can be used to generate parameterized fractal noise based on Open Simplex.

NoiseTexture uses SimplexNoise to generate noise textures for using in
shaders/visual effects.

thirdparty/README.md

@@ -356,6 +356,11 @@ Collection of single-file libraries used in Godot components.
   * Upstream: https://github.com/ivanfratric/polypartition (`src/polypartition.cpp`)
   * Version: TBD, class was renamed
   * License: MIT
+- `open-simplex-noise.{c,h}`
+  * Upstream: https://github.com/smcameron/open-simplex-noise-in-c
+  * Version: git (0d555e7, 2015)
+  * License: Unlicense
+
 
 ### modules