gnu: Add emacs-company.

* gnu/packages/emacs.scm (emacs-company): New variable.

gnu: certbot, python-acme: Update to 0.8.1.

These packages should be updated together.

* gnu/packages/tls.scm (certbot): Update to 0.8.1.
(python-acme, python2-acme): Update to 0.8.1

gnu: aria2: Update to 1.24.0.

* gnu/packages/bittorrent.scm (aria2): Updat eto 1.24.0.

services: dicod: Add 'interfaces' configuration field.

This makes 'dicod' listen on 'localhost' by default, whereas it was
previously listening on all the interfaces, which is not a good default
security-wise.

* gnu/services/dict.scm (<dicod-configuration>)[interfaces]: New field.
(dicod-configuration-file)[database->text]: New procedure, with code
formerly in 'dicod-configuration->text'.
[dicod-configuration->text]: Rename to...
[configuration->text]: ... this.  Honor 'interfaces'.
* doc/guix.texi (Various Services): Document 'interfaces'.

gnu: libqtxdg: Move qtbase to propagated-inputs.

* gnu/packages/lxqt.scm (libqtxdg)[inputs]: Move qtbase ...
[propagated-inputs]: ... to here.

This is a follow-up to aa450b2bc41b0cedbebc4f8c0a51867a436cf02b.

gnu: enlightenment: Update to 0.20.9.

* gnu/packages/enlightenment.scm (enlightenment): Update to 0.20.9.
[home-page]: Use https.

gnu: python-efl: Rebuild generated C files.

* gnu/packages/enlightenment.scm (python-efl)[arguments]: Replace 'build
phase to set 'ENABLE_CYTHON=1'.
[native-inputs]: python-cython.

gnu: Add python-bz2file.

* gnu/packages/python.scm (python-bz2file, python2-bz2file): New
variables.

gnu: gnupg: Update to 2.1.13.

* gnu/packages/gnupg.scm (gnupg): Update to 2.1.13.

Signed-off-by: Leo Famulari <leo@famulari.name>

utils: 'current-source-directory' returns the absolute directory name.

* guix/utils.scm (current-source-directory): When FILE-NAME is relative,
use 'search-path' to determine the absolute file name.

utils: 'current-source-directory' is now purely an expansion-time thing.

* guix/utils.scm (extract-directory): Remove.
(current-source-directory): Rewrite as a 'syntax-case' macro.

doc: Recommend against marketing phrases in descriptions.

* doc/guix.texi (Synopses and Descriptions): Add note about marketing
phrases.

gnu: lxqt-common: Add missing inputs.

* gnu/packages/lxqt.scm (lxqt-common)[inputs]: Add qtbase,
qttools, qtx11extras.

gnu: lxqt-session: Add missing inputs.

* gnu/packages/lxqt.scm (lxqt-session)[inputs]: Add qtbase,
qttools, qtx11extras.

gnu: liblxqt: Add missing inputs.

* gnu/packages/lxqt.scm (liblxqt)[inputs]: Add qtbase,
qttools, qtx11extras.

gnu: libqtxdg: Build with qtbase.

* gnu/packages/lxqt.scm (libqtxdg)[propagated-inputs]: Remove qt.
[inputs]: Add qtbase.

gnu: lxqt: Update uris.

* gnu/packages/lxqt.scm (libqtxdg, liblxqt, lxqt-common,
lxqt-session)[source]: Project tarballs have been replaced with Github
archive tarballs.

gnu: starman: Update to 0.4014.

* gnu/packages/web.scm (starman): Update to 0.4014.

gnu: calibre: Build with qtbase.

* gnu/packages/ebook.scm (calibre)[inputs]: Remove qt, add qtbase.
[native-inputs]: Remove qt, add qtbase.

gnu: avidemux: Build with modular qt.

* gnu/packages/video.scm (avidemux)[inputs]: Remove qt, add qtbase, qttools.