• Add heman_generate_planet_heightmap, which samples noise over a 3D domain to generate a lat-long height field for an imaginary planet.

• Added Sphinx documentation.
• Added the ability to build with double instead of float.
• Lots of naming changes to move functions into "namespaces" that make more sense.

This is the birth of heman, a tiny C library for doing stuff with height fields, distance fields, and normal maps.