Improved Textures

### 2.6.8 Improved Textures

- Nine new patterns are added.
- New warps are added, cylindrical, spherical, toroidal and planar mapping.
- Texturing the difference: cutaway_textures.
- Give the interior an other texture than the exterior: interior_texture.
- Triangle texture interpolation, using a list of textures.
- More natural light behavior for transparent objects with reflection: conserve_energy.
- More natural reflection and a new finish reflection{} block. Adding fresnel reflection and manually controlled 'angle dependent' reflection.
- Normal accuracy keyword for more control.
- Keeping control over the bump height: normal no_bump_scale.
- Filter now also works as `filter` in layered textures.
- Transmit now works consistent inside as well as outside the 0 - 1 range.