gnu: Add emacs-jsonrpc.

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

gnu: guile-gi: Update to 0.3.0.

* gnu/packages/guile-xyz.scm (guile-gi): Update to 0.3.0.

gnu: Add gtksheet.

* gnu/packages/gtk.scm (gtksheet): New variable.

gnu: toxic: Fix build with Python 3.8.

* gnu/packages/messaging.scm (toxic)[arguments]: Add substitution in the
enable-python-scripting phase.

gnu: emacs-evil-collection: Update to 20200509.

* gnu/packages/emacs-xyz.scm (emacs-evil-collection): Update to 20200509.

gnu: emacs-helm-fish-completion: Update to 0.3.

* gnu/packages/emacs-xyz.scm (emacs-helm-fish-completion): Update to 0.3.

gnu: ccid: Update to 1.4.32.

* gnu/packages/security-token.scm (ccid): Update to 1.4.32.

gnu: rocksdb: Update to 6.8.1.

* gnu/packages/databases.scm (rocksdb): Update to 6.8.1.

gnu: fluidsynth: Update to 2.1.2.

* gnu/packages/audio.scm (fluidsynth): Update to 2.1.2.

gnu: wavpack: Update to 5.3.0.

* gnu/packages/audio.scm (wavpack): Update to 5.3.0.

gnu: xmlsec: Update to 1.2.30.

* gnu/packages/xml.scm (xmlsec): Update to 1.2.30.

gnu: maim: Update to 5.6.3.

* gnu/packages/xdisorg.scm (maim): Update to 5.6.3.

gnu: slop: Update to 7.5.

* gnu/packages/xdisorg.scm (slop): Update to 7.5.

gnu: openh264: Update to 2.1.0.

* gnu/packages/video.scm (openh264): Update to 2.1.0.
[source]: Change to GIT-FETCH.

gnu: mbedtls-apache: Update to 2.16.6.

* gnu/packages/tls.scm (mbedtls-apache): Update to 2.16.6.

gnu: ceph: Update to 14.2.9.

* gnu/packages/storage.scm (ceph): Update to 14.2.9.

gnu: msmtp: Update to 1.8.10.

* gnu/packages/mail.scm (msmtp): Update to 1.8.10.

gnu: feh: Update to 3.4.

* gnu/packages/image-viewers.scm (feh): Update to 3.4.

gnu: rtl-sdr: Improve description.

* gnu/packages/radio.scm (rtl-sdr)[description]: Add instructions for
  blacklisting the default rtl28xxu DVB Linux driver.

gnu: asymptote: Fix build.

* gnu/packages/plotutils.scm (asymptote)[native-inputs]: Add texlive-etoolbox.