[Groff] revised color support

[Werner LEMBERG]

I've just checked in the new color support for groff, together with
Bernd's revision of the intermediate output parser.  Please test.
Note that grohtml's color implementation currently fails; I've already
informed Gaius to fix that (which is probably rather trivial for him).
Now it formats Rick's `colbug' man pages correctly.

groff_out(7) describes the new intermediate color format; the only
user-visible change in troff is the introduction of a device-specific
`default' color name.

It should now be rather straightforward to add color support to
grotty.


    Werner