bug#26560: [PATCH] build: emacs: Install only a subset of files.

[Arun Isaac <arunisaac@systemreboot.net>]

This is a work in progress patch for the discussion at
https://lists.gnu.org/archive/html/guix-devel/2017-04/msg00274.html

All feedback welcome!

Arun Isaac writes:

> +                      (include ''(".*.el$" ".*.el.in$" "^dir$"
> +                                 ".*.info$" ".*.texi$" ".*.texinfo$"
> +                                 "doc/dir" "doc/*.info$" "doc/*.texi$" "doc/*.texinfo$"))
> +                      (exclude ''("^.dir-locals.el$" "^test.el$" "^tests.el$" ".*-test.el$" ".*-tests.el$"))

I've copied all this from MELPA's default :files property described at
https://github.com/melpa/melpa . I have no idea what the rationale for
some of these regexes are.

Currently, include and exclude are a list of regexes that file names are
matched against. Should this be combined into one big regex?

Would it be a good idea to add a third keyword argument, say
#:documentation, that will select info documentation files and install
them separately in some other directory?