* emacs/guix-guile.el (guix-guile-keyword-regexp): New function.
* emacs/guix-devel.el (guix-devel-faces): New custom group.
(guix-devel-modify-phases-keyword): New face.
(guix-devel-modify-phases-keyword-regexp,
guix-devel-font-lock-keywords): New variables.
(guix-devel-modify-phases-font-lock-matcher,
guix-devel-modify-phases-font-lock-pre): New functions.
(guix-devel-mode): Adjust to add/remove font-lock-keywords.
Suggested by Ludovic Courtès <ludo@gnu.org>.
* emacs/guix-guile.el (guix-guile-definition-regexp): New variable.
(guix-guile-current-definition, guix-guile-boolean): New functions.
* emacs/guix-devel.el: Require 'guix-base'.
(guix-devel-repl-processes): New variable.
(guix-devel-setup-repl, guix-devel-setup-repl-maybe): New functions.
(guix-devel-build-package-definition): New command.
* doc/emacs.texi (Emacs Development): Document it.
* emacs/guix-guile.el (guix-guile-current-module): New function.
* emacs/guix-devel.el: New file.
* emacs.am (ELFILES): Add it.
* doc/emacs.texi (Emacs Development): New node.
(Emacs Interface): Add it.
* doc/contributing.texi (The Perfect Setup): Mention it.
* doc/guix.texi (Top): Add it.
* emacs/guix-init.el: Add 'guix-devel-activate-mode-maybe' to
'scheme-mode-hook'.
* emacs/guix-backend.el (guix-make-guile-expression): Move to...
* emacs/guix-guile.el: ... here. New file.
* emacs/guix-base.el: Use it.
* emacs/guix-command.el: Use it.
* emacs.am (ELFILES): Add it.
