Add Spotlight indexes to gitignore
Many changes.

- remove buggy zrot (Blender renderer, fern example)
- Fern example:
  * Unify turning (left/right no longer separate)
  * Completely uniform spacing of branches
  * Some randomisation of turning angles (using Gaussian distribution)
  * Merge pushing/popping of length stack and transformation stack
- GL Renderer:
  * Allow choosing colours and line thickness
Merge remote-tracking branch 'origin/master'

Conflicts:
	lsys/example/fern.py