Set the 'indoor_light' property (for new DOOM CSG code)
brushlib : only have one parameter to Trans.brush() -- assume caller will
take care of setting the brush kind.
Render : set "sky" mode on outdoor _SKY ceiling brushes.
Layout : fixed a few bugs with new shadow code.
Outdoor shadows : changed angle of sun, instead of exactly SW it is now
close to SSW (x delta -64, y delta -128), which looks a bit better.
Outdoor shadows : better logic to decide where to place them (esp. at the
walls which separate zones).
Utilities : added geom.unit_vector() function
Utils : added bezier curve functions: bezier_coord() and bezier_tangent()
Utils : added function to compute approx length of a bezier curve.
Area / group rooms : size tweak.
Connect : improved the code for handling hallways.
brushlib : added 'set_kind()' function.
Removed "straddle" as a possible border kind.
Room class : tweaked tostr() method.
Room class : added sanity check to kill_it() method.
Connect : fixed some bugs in hallway processing.
Area : improved logic for handling TINY areas, in particular allow merging
into a nearby hallway when killing the area is not completely safe.
Ensure touching hallway areas become a single room (or in other words, two
hallway rooms will never touch each other).  The connection logic depends
on this.