and now _removing_ the edge deformation data

pending a better understanding of precisely how i want that to work
fixed emittence calculations i think
spun rhombic coordinates out into their own file
spun material settings out into their own Material module

(since very soon there's gonna be things aside from cells needing
material data)
added sphere primitive generation
`:: (g -> (a, g) -> Rand g a` & consequential code simplification

b/c passing that random value around during world gen was kind of
ridiculous
wrote tetrahedron-octahedron coordinate code + converters to & from rhombic dodecahedron format

short version, this makes it possible to make unique references to
_vertices_ on the map, instead of muddling around with like,
(coordinate, vertex index) representations.
put a limiter on light casts, based on total luminance hitting the target

(don't even bother trying to raycast if the light is far enough away
that there's close to zero illumination)