More couples for the matching_pairs option

Last year, this commit introduced the matching_pairs option to be used with the m key.

By default, it offers the 4 following couples that are suitable for programming: ( ) { } [ ] < >

While editing prose document, I believe that other common typographic pairs can be useful to append:

set -add global matching_pairs « » “ ” ‘ ’

Note that in some countries, as described here
some variations may occurs like „ “ in central Europe.

And now, thanks to laelath, the show_matching highlighter honors the couples in the matching_pairs option. Great!