bug#36883: Make Gnus documentation clearer ("dumbquotes")

[Keith Thompson]

Emacs 26.2.90, Gnus v5.1

The Gnus info documentation includes the following:

‘W d’
     Treat M****s*** sm*rtq**t*s according to
     ‘gnus-article-dumbquotes-map’ (‘gnus-article-treat-dumbquotes’).
     Note that this function guesses whether a character is a sm*rtq**t*
     or not, so it should only be used interactively.

     Sm*rtq**t*s are M****s***’s unilateral extension to the character
     map in an attempt to provide more quoting characters.  If you see
     something like ‘\222’ or ‘\264’ where you’re expecting some kind of
     apostrophe or quotation mark, then try this wash.

I suggest changing "M****s***" to "Micrsoft" and "sm*rtq**t*s" to "smartquotes"
throughout.

I'd also suggest changing the command names "article-treat-dumbquotes"
and "gnus-article-treat-dumbquotes" to refer to "smartquotes" rather than
"dumbquotes", probably keeping the existing names as aliases.

IMHO documentation should make it easy to search without being
an obstacle to understanding. I don't object to snark, but it shoudn't
come at the expense of clarity.