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Things to come Before real 4.0
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Cache shadowing information when shadowtransp is true.

Make shadowtransp the default; replace 'shadowtransp' keword
with 'solidshadow' keyword.

If World object has only one subobject, and the World
is neither textured nor transformed (can't do this anyway),
then make that object the World object.  In theory we could
do this throughout the modeling tree.

> 2 objects in CSG objects

Create nasty, rigorous test scenes, more examples in general.

Put Linda code back in place.

User-selectable primitives/aggregates/lights/textures at compile time?

Technical Documentation

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Eventually
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Make heightfields be stored in fixed-point, and take care of byte-ordering
problems so that height fields are transportable from machine to machine.

Is Bayes' theorem-based polygon intersection method better?

Implement something similar to Jevans & Wyvill's adaptive subdivision scheme.

Add better antialiasing (e.g., Mitchell's paper).

Add an option to perform sorting during ray/List intersection tests so
objects are tested approximately in order.
