[Groff] filled polygons in pic

[Doug McIlroy]

Have filled polygons been considered as a pic capability?
It appears that all the infrastructure is in place and only needs
a simple syntax, like "poly from A to B to C".

I made a filled right triangle by editing out one corner
of a box in pic output, and of course any polygon can be
broken down into right triangles ... but this is madness.
It it seems like a good idea, I might volunteer to try to
do it right.

Doug McIlroy