seg faults

Raycasting fails at vertices. (t_hit is inf)
Switch from vertices to triangle centers - Raycasting still fails (t_hit is inf)

Remove SelectVisible (implementation was incorrect).
Instead use visibility map for each texel directly.
Add pixel_foreshortening
Python test example by rendering images and using them to project albedo.

Documentation
Cleanup
Add download for Baluster vase model in python example.

Needs tbb::feeder from tbb::parallel_for_each

Mostly works - slight issues
Image::Resize for Bool has bus error / seg fault.
highlights detection doesn't work.