* Option presets, for demonstration.
* Continously average samples across multiple frames
so you can render more than your GPU can handle in one go.
* Saturation correction for overly-bright pixels.
* Freeze and loop time.
* Settings for TAA, camera position, and aspect ratio cropping.
Added a ton of comments & docs, refactored, and *hopefully* now support
medium/medium transitions and nested media well enough to work.
Haven't tested that part yet, though.
Also tiled/clamped perspective projection, temporal antialiasing,
a real camera, and tons of path marching-related features
which haven't yet been used to their fullest potential.
James T. Martin