1. Wrote introduction and advanced topic bump mapping in README.md.
2. Gave asteroids random rotations.
3. Use a better cobble_normal.tga normal map.
4. Now there are 3 different asteroid geometries with 3 different normal maps.
5. Note: collision detection works poorly with the elongated asteroid because
it is not a sphere but a bounding sphere is still used for collision detection.
Merged MoreAsteroids. Changed some normal map tga files.