* emacs/guix-command.el (guix-command-improve-environment-argument): Use
"E" for '--expose' and "S" for '--share' to distinguish them from
'--expression' and '--system' accordingly. Make '--ad-hoc' an option
taking packages instead of a simple switch.
(guix-command-rest-argument): Complete shell command instead of
packages for '--' argument.
(guix-command-additional-arguments): Add fake 'packages' argument.
New variable.
(guix-command-additional-arguments): Use it.
(guix-command-post-process-environment-packages,
guix-command-post-process-environment-ad-hoc): New functions.
(guix-command-post-processors): Add "environment" command with the new
argument processors.
* emacs/guix-command.el (guix-command-improve-action-argument): Use "C"
key for 'container' action to distinguish it from 'challenge'.
(guix-command-rest-argument): Add positional arguments.
* 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.
* emacs/guix-base.el (guix-package-location): New function.
(guix-edit-package): Rename and move to ...
* emacs/guix.el (guix-edit): ...here. Make it interactive.
* emacs/guix-command.el (guix-edit-action): New function (alias to
'guix-edit') to override the popup for edit command in "M-x guix".
* emacs/guix-list.el (guix-list-edit-package): Adjust for 'guix-edit'
renaming.
* emacs/guix-main.scm (package-location-string): Allow to accept package
id or package name as argument.
