Jan 14, 2016
Small changes to interactive mode
- Add 'fullscreen' flag to GlobalSettings. This way, going fullscreen
  in interactive mode is optional, and actually defaults to false.
- The movement/rotation parameters in the interactive mainloop aren't
  fixed, so your "movement speed" no longer depends on how long it
  takes for a frame to render. Instead, the last frame render time is
  used to scale the constants, so now movement/lookaround behaves
  more predictably.
Jan 13, 2016
Eliminate some divisions in BBox intersection methods.
Since divisions by ray.dir.(x|y|z) happen a lot, it's beneficial to
compute the reciprocal of ray.dir before the intersection calculation.
This is made with a special, augmented Ray class (RRay).

The same kind of optimization can be implemented in other parts of the
raytracer, but doing it globally makes no sense: RRay::dir and rdir have
to be kept in sync, which is too much work to do (esp. through
model-view transformations).

This optimization sheds about 1.5% of the render time.
Jan 12, 2016
Test scene for homework tasks after Lecture 12.
Jan 10, 2016
Preparations for Homework10: sync project files, add scene in data/hw10.
Jan 6, 2016
Fix errors/warnings under MSVC.
Dec 9, 2015
Scene for homework6, group 2.
Dec 7, 2015
Add support for making screenshots (use the F12 key).