I'm back to visualzing how to display XCOM-like thin walls in a curses
display.  My prior idea (UNICODE, magnify the squares and use box-
drawing along the grid lines) only looked good; it isn't playable on a
24x80 console thanks to a pathetic on-screen view radius of 5.  So
that won't get released.  ["One main() To Rule Them All" is working
out very well emotionally.  Aside from having to convert
destroy_renderer() into an atexit handler to make the game survive the
Close button, it looks like it is going to work as intended.]

My best guess now is to focus on visibility:
* use bolded colors for squares in direct view
* use faded colors for squares not in direct view
* don't bother showing thin-walls directly (they manifest by chopping
off visibility).

This doesn't handle windows inset into walls gracefully, unlike the
UNICODE approach.