"Grand structure of Lasercake" updates

[Isaac Dupree]

This new world is a mesh of tetrahedra...

Implemented: wireframe display of the mesh (display() and do_gl()),
sanity-checking (debug_check_consistency()), and a default hard-coded
world (constructor grand_structure_of_lasercake()).

-Isaac

[Isaac Dupree]

Pushed. If you want it to display any moment other than 7 picoseconds,
you'll have to change do_gl() to pass a different time (perhaps based on
'frame' somehow).

The computation of a vertex's location at a given time (in display())
currently rounds the time moment to milliseconds. I don't know about
runtime overflow, but the compile-time boost::ratio in the units types
overflowed when I multiplied nanometers/second by picoseconds! This
deserves to be improved somehow.

-Isaac