[Groff] SGR implementation in groff

[Werner LEMBERG]

I'm going to implement SGR support in the TTY output of groff -- since
groff now supports colors (HTML and PS output already have it), the
switch is necessary.

Some remarks:

  . I intend to handle SGR escapes similar to the handling of
    character set changes in Emacs.  This means that at the end of a
    line, the state is always reset to the default.  BTW, `less'
    version 358 doesn't work correctly (with the -R option) if this
    isn't done, so I have just another reason to do so (besides to
    avoid states crossing the line border).

  . SGR will be the default; grotty's current output for bold and
    underlining will be available if the `-c' switch is selected to
    suppress color output.

  . The -u switch of grotty will be used in SGR mode to decide whether
    italic characters shall be drawn as underlined (the default) or as
    real italic characters.  Consequently, the options -b, -B, and -U
    take no effect in SGR mode.

  . The escape \M will directly work with grotty to set the background
    color for the forthcoming text.  This is different to PS output
    which will use \M only for objects drawn with \D (grohtml has no
    support for \M yet).


Comments?


    Werner