emacs: Add API for 'guix-entry'.

* emacs/guix-info.el: Use new entry procedures.
* emacs/guix-list.el: Likewise.
* emacs/guix-base.el: Likewise.
  (guix-get-entry-by-id): Move and rename to ...
* emacs/guix-entry.el (guix-entry-by-id): ...this.  New file.
  (guix-entry-value, guix-entry-id, guix-entries-by-ids)
  (guix-replace-entry): New procedures.
* emacs.am (ELFILES): Add new file.

emacs: Add 'guix-with-indent'.

* emacs/guix-utils.el (guix-with-indent): New macro.
  (guix-memoized-font-lock-keywords): Rename to...
  (guix-utils-font-lock-keywords): ... this.  Add it.
* emacs/guix-info.el (guix-info-insert-entry-default): Use it.

emacs: Use "cl-list*" instead of "apply #'list".

* emacs/guix-command.el (guix-run-view-build-log): Use cl-list*.
  (guix-run-view-size-map): Likewise.
* emacs/guix-external.el (guix-dot-arguments): Likewise.

gnu: Add python-markdown.

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

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

gnu: love: Update to 0.10.0.

* gnu/packages/game-development.scm (love): Update to 0.10.0.

gnu: guile-ssh: Update to 0.9.0.

* gnu/packages/ssh.scm (guile-ssh): Update to 0.9.0.

system: Allow the root file system to be named by UUID.

* gnu/build/file-systems.scm (canonicalize-device-spec)[canonical-title]:
Use 'string->uuid' to check whether SPEC is a UUID.
When SPEC is a string and CANONICAL-TITLE is 'uuid, call 'string->uuid'.
* gnu/system.scm (operating-system-grub.cfg): Add 'root-device'
variable and use it for the "--root=" argument.

file-systems: Move 'string->uuid' to the build side.

* gnu/system/file-systems.scm (%uuid-rx, string->uuid): Move to...
* gnu/build/file-systems.scm (%uuid-rx, string->uuid): ... here.  New
variables.

system: Allow the root file system to have a UUID.

This is a followup to ab64483.

* gnu/system.scm (mapped-device-user): Check whether the title of FS is
'device before calling 'string=?'.
* gnu/system/vm.scm (virtualized-operating-system)[user-file-systems]:
Likewise.

doc: Mention how to verify signatures.

* doc/guix.texi (Binary Installation): Be more precise about signature
verification.  Suggested by Carl Hansen <carlhansen1234@gmail.com>.

gnu: Add xaos.

* gnu/packages/maths.scm (xaos): New variable.

Signed-off-by: Alex Kost <alezost@gmail.com>

gnu: Move cursynth to (gnu packages music).

* gnu/packages/cursynth.scm: Remove.
* gnu/packages/music.scm (cursynth): New variable, from cursynth.scm.
* gnu-system.am (GNU_SYSTEM_MODULES): Remove cursynth.scm.

gnu: libcue: Update source URL.

* gnu/packages/cdrom.scm (libcue)[source]: Update URL.

gnu: python-mox3: Update to 0.13.0.

* gnu/packages/openstack.scm (python-mox3): Update to 0.13.0.

gnu: python-fixtures: Update to 1.4.0.

* gnu/packages/python.scm (python-fixtures): Update to 1.4.0.

gnu: python-pyld: Update to 0.6.8.

* gnu/packages/python.scm (python-pyld): Update to 0.6.8.

gnu: python-virtualenv: Update to 13.1.2.

* gnu/packages/python.scm (python-virtualenv): Update to 13.1.2.
[arguments]: Custom test command.
[inputs]: Remove python-nose, add python-pytest.

gnu: python-oslosphinx: Update to 4.2.0.

* gnu/packages/openstack.scm (python-oslosphinx): Update to 4.2.0.

gnu: python-oslo.serialization: Update to 2.2.0.

* gnu/packages/openstack.scm (python-oslo.serialization): Update to 2.2.0.

gnu: python-os-testr: Update to 0.5.0.

* gnu/packages/openstack.scm (python-os-testr): Update to 0.5.0.