emacs: Add help variables.
* emacs/guix-pcomplete.el (guix-pcomplete-parse-package-regexp,
guix-pcomplete-parse-command-regexp,
guix-pcomplete-parse-long-option-regexp,
guix-pcomplete-parse-short-option-regexp,
guix-pcomplete-parse-list-regexp, guix-pcomplete-parse-regexp-group,
guix-pcomplete-systems, guix-pcomplete-hash-formats,
guix-pcomplete-refresh-subsets, guix-pcomplete-key-policies): Move and
rename to ...
* emacs/guix-help-vars.el (guix-help-parse-package-regexp,
guix-help-parse-command-regexp, guix-help-parse-long-option-regexp,
guix-help-parse-short-option-regexp, guix-help-parse-list-regexp,
guix-help-parse-regexp-group, guix-help-system-types,
guix-help-hash-formats, guix-help-refresh-subsets,
guix-help-key-policies): ...here. New file.
(guix-help-parse-option-regexp, guix-help-source-types,
guix-help-verify-options, guix-help-elpa-archives): New variables.
* emacs.am (ELFILES): Add "guix-help-vars.el".