* 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'.
* guix/scripts/size.scm: New file.
* Makefile.am (MODULES): Add it.
(SCM_TESTS): Add tests/size.scm.
* doc.am (SUBCOMMANDS): Add 'size'.
* po/guix/POTFILES.in: Add guix/scripts/size.scm.
* tests/size.scm: New file.
* doc/guix.texi (Packages with Multiple Outputs): Add xref to "Invoking guix
size".
(Invoking guix size): New node.
(Invoking guix gc): Add index for "closure" and xref to the above.
* doc/contributing.texi (Submitting Patches): Use @enumerate for the check
list. Add item about 'guix size'.
* HACKING (Contributing): New section.
(Building from Git, The Perfect Setup, Coding Style, Submitting Patches):
Move to ...
* doc/guix.texi (Running Guix Before It Is Installed): Likewise.
* doc/contributing.texi: ... here. New file.
* doc.am (EXTRA_DIST): Use it.
* README (Installation): Adapt to it.
* configure.ac (DOT): Likewise.
