ui: Add package-description-string.

Provide support for Texinfo's markup in package description.

* guix/ui.scm (%text-width): New parameter.
  (texi->plain-text): New variable.
  (package->recutils): Use them.
  (package-description-string): New variable.
* emacs/guix-main.scm (%package-param-alist): Use it.
* gnu/packages/perl.scm (perl-devel-globaldestruction)
  (perl-devel-lexalias, perl-exporter-lite): Adapt to Texinfo's markup.
* gnu/packages/python.scm (python2-empy): Likewise.

emacs: Add support for "triplet" package inputs.

Fixes <http://bugs.gnu.org/21399>.

* emacs/guix-main.scm (full-name->name+version): Adjust to handle
  "name-version:output" string.
  (package-inputs-names): Support ("name" package "output") inputs.

emacs: Use "r" key for 'cran' action in 'import' popup.

* emacs/guix-command.el (guix-command-improve-import-argument): New
  variable and function.
  (guix-command-argument-improvers): Add it.

emacs: Add "View graph" action to graph popup.

* emacs/guix-command.el: Require 'guix-external'.
  (guix-run-view-graph): New function.
  (guix-command-additional-execute-arguments,
  guix-command-special-executors): Add entries for "View graph" action.

emacs: Allow users to choose a 'find-file' function.

* emacs/guix-utils.el (guix-find-file-function): New variable.
  (guix-find-file): Use it.

emacs: Add code to run 'dot' program.

* emacs/guix-external.el: New file.
* emacs.am (ELFILES): Add it.

emacs: Add code to pipe guix output to external program.

* emacs/guix-main.scm: Use (ice-9 popen) module.
  (pipe-guix-output): New procedure.

emacs: Use only one guix-load-path variable.

emacs/guix-init.el (guix-load-path): Move to ...
emacs/guix-backend.el (guix-load-path): ... Here. Redefine it.

emacs: Fix guix-guile-program default value.

Fixes <http://bugs.gnu.org/21127>.

* emacs/guix-backend.el: Use guix-config.
  (guix-guile-program): Move to ...
* emacs/guix-config.el.in (guix-guile-program): ... here.  Use Guile
  program file name from compile-time instead of depending on PATH.

build: Produce 'guix-config' instead of using compile-time tricks.

* emacs/guix-{init,profiles}.el.in: Rename to ...
* emacs/guix-{init,profiles}.el: ... these.  New files.
  Use 'guix-config'.
* emacs/guix-config.el.in: New file.
* emacs.am (nodist_lisp_DATA): Add it.  Move them to ...
  (ELFILES): ... here.
* .gitignore, configure.ac: Adjust accordingly.

emacs: Use prompt for packages instead popup for edit action.

* 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.

emacs: Add popup interface for guix commands.

* emacs/guix-command.el: New file.
* emacs.am (ELFILES): Add it.
* doc/emacs.texi (Emacs Initial Setup): Mention 'magit-popup' library.
  (Emacs Popup Interface): New node.
  (Emacs Interface): Add it.
* doc/guix.texi (Top): Likewise.

emacs: Add "guix-popup.el".

* emacs/guix-popup.el: New file.
* emacs.am (ELFILES): Add it.

emacs: Add code to run guix command in shell.

* emacs/guix-base.el (guix-run-in-shell, guix-run-in-eshell,
  guix-run-command-in-shell): New functions.
  (guix-run-in-shell-function, guix-shell-buffer-name): New variables.

emacs: Add code to run guix command in REPL.

* emacs/guix-base.el (guix-run-command-in-repl, guix-command-output,
  guix-help-string): New functions.
* emacs/guix-main.scm (guix-command, guix-command-output, help-string):
  New procedures.

emacs: Add and use alist accessors.

* emacs/guix-utils.el (guix-define-alist-accessor): New macro.
  (guix-assq-value, guix-assoc-value): New functions.
  (guix-get-key-val): Remove.
* emacs/guix-base.el: Replace 'guix-get-key-val' with 'guix-assq-value'
  everywhere.
* emacs/guix-info.el: Likewise.
* emacs/guix-list.el: Likewise.
* emacs/guix-messages.el: Likewise.

emacs: Add minibuffer readers.

* emacs/guix-read.el: New file.
* emacs.am (ELFILES): Add it.

emacs: Add help variables.

* emacs/guix-pcomplete.el (guix-pcomplete-parse-package-regexp,
  guix-pcomplete-parse-command-regexp,
  guix-pcomplete-parse-long-option-regexp,
  guix-pcomplete-parse-short-option-regexp,
  guix-pcomplete-parse-list-regexp, guix-pcomplete-parse-regexp-group,
  guix-pcomplete-systems, guix-pcomplete-hash-formats,
  guix-pcomplete-refresh-subsets, guix-pcomplete-key-policies): Move and
  rename to ...
* emacs/guix-help-vars.el (guix-help-parse-package-regexp,
  guix-help-parse-command-regexp, guix-help-parse-long-option-regexp,
  guix-help-parse-short-option-regexp, guix-help-parse-list-regexp,
  guix-help-parse-regexp-group, guix-help-system-types,
  guix-help-hash-formats, guix-help-refresh-subsets,
  guix-help-key-policies): ...here.  New file.
  (guix-help-parse-option-regexp, guix-help-source-types,
  guix-help-verify-options, guix-help-elpa-archives): New variables.
* emacs.am (ELFILES): Add "guix-help-vars.el".

emacs: Add 'guix-package-names'.

* emacs/guix-main.scm (package-names, package-names-lists): New procedures.
* emacs/guix-base.el (guix-package-names): New function.

emacs: Add 'guix-graph-type-names'.

* emacs/guix-main.scm: Use (guix scripts graph) module.
  (graph-type-names): New procedure.
* emacs/guix-base.el (guix-graph-type-names): New function.