* emacs/guix-backend.el (guix-before-repl-operation-hook,
guix-after-repl-operation-hook, guix-repl-operation-p): New variables.
(guix-repl-operation-success-message, guix-repl-output-filter): New
procedures.
(guix-start-repl): Adjust for using 'guix-repl-output-filter'.
(guix-eval-in-repl): Honor 'guix-before-repl-operation-hook'.
* configure.ac (emacsuidir): New variable.
(AC_CONFIG_FILES): Add 'emacs/guix-init.el', 'emacs/guix-helper.scm'.
* Makefile.am: Include 'emacs.am'.
* emacs.am: New file.
* doc/emacs.texi: New file.
* doc/guix.texi: Include 'emacs.texi'.
* emacs/guix-backend.el: New file.
* emacs/guix-base.el: New file.
* emacs/guix-helper.scm.in: New file.
* emacs/guix-history.el: New file.
* emacs/guix-info.el: New file.
* emacs/guix-init.el.in: New file.
* emacs/guix-list.el: New file.
* emacs/guix-main.scm: New file.
* emacs/guix-utils.el: New file.
* emacs/guix.el: New file.
