[m-dev.] where to document color schemes

[Zoltan Somogyi]

The option --color-scheme and the envvar MERCURY_COLOR_SCHEME
both need to document the syntax we use for color schemes.
I could include the documentation of color schemes in either
the documentation of the option or the documentation of the envvar,
with a pointer from the other, but neither feels right, partially because
of the asymmetry, and partially because describing what color schemes *are*
and how they can be specified requires much longer text than the
documentation of pretty much all other options and envvars.
(I know, because I have been writing it today.)

Would anyone object if I documented color schemes in a new
section of the user guide, probably added after the current section 10
which is Environment variables, with a link there from both the option
and the envvar? I am thinking calling it "Color in diagnostics",
and it would explain both color schemes and the algorithm we use
to decide whether to use colors at all.

Does anyone have a better idea?

Zoltan.