Update docutils to 0.18

[pyup-bot]

This PR updates docutils from 0.17.1 to 0.18.

Changelog

0.18b1

===========================

.. Note::

Docutils 0.18.x is the last version supporting Python 2.7 and 3.5.


* Output changes:

Identifiers:
 During `identifier normalization`_, leading number and hyphen
 characters are no longer stripped from a `reference name`_, if the
 id_prefix_ setting is non-empty.

 Example:
   with ``--id-prefix="DU-"``, a section with title "34. May"
   currently gets the identifier key ``DU-may`` and after the
   change the identifier key ``DU-34-may``.

 The default value for the auto_id_prefix_ setting changed to ``%``:
 "use the tag name as prefix for auto-generated IDs".
 Set auto_id_prefix_ to ``id`` for unchanged auto-IDs.

HTML5:
 Use the semantic tag <aside> for footnote text and citations, topics
 (except abstract and toc), admonitions, and system messages.
 Use <nav> for the Table of Contents.

 Make "auto" table column widths the default: Only specify column
 widths, if the `"widths" option`_ is set and not "auto".
 The table-style__ setting "colwidths-grid" restores the current default.

 .. _"widths" option: __ docs/ref/rst/directives.htmltable
 __ docs/user/config.htmltable-style

 Items of a definition list with class argument "details" are
 converted to `details disclosure elements`_. Example::

   ..class:: details

   Summary
     This additional information should be hidden.

 Do not add "compound-first", "compound-middle", or "compound-last" to
 elements nested in a compound. Use child selector and ":first-child",
 ":last-child" pseudo classes instead.
 Use class value "backrefs" instead of "fn-backref" for a span of
 back-references.

 Write footnote brackets and field term colons to HTML, so that they
 are present also without CSS and when copying text.

 Move space character between section number and heading into
 "sectnum" span.

math-output: html
 Support more commands, fix mapping of commands to Unicode characters.
 Scale variable sized operators and big delimiters with CSS.
 Don't use <tt> element (deprecated in HTML5).
 Use STIX fonts if available.

LaTeX:
  `legacy_class_functions`_ setting default changed to "False":
  admonitions are now environments.

* New standard Docutils doctree node "meta__".

* New configuration setting: [latex writers] legacy_column_widths_.

* Removed files:

- ``iepngfix.htc`` and ``blank.gif`` (IE 6 workaround for `s5_html`).

* Removed function: ``utils.unique_combinations``
(obsoleted by ``itertools.combinations``).

* Removed attribute: ``HTMLTranslator.topic_classes``
(check node.parent.classes instead).

* Major refactoring and fixes/additions in
``docutils/utils/math/math2html.py`` and
``docutils/utils/math/latex2mathml.py``
(mathematical notation in HTML, cf. `LaTeX syntax for mathematics`_).

* ``nodes.Node.traverse()`` returns an iterator instead of a list.

* Various bugfixes and improvements (see HISTORY_).

__ docs/ref/doctree.htmlmeta
.. _identifier normalization:
docs/ref/rst/directives.htmlidentifier-normalization
.. _id_prefix: docs/user/config.htmlid-prefix
.. _auto_id_prefix: docs/user/config.htmlauto-id-prefix
.. _details disclosure elements:
 https://www.w3.org/TR/html52/interactive-elements.html#the-details-element
.. _LaTeX syntax for mathematics: docs/ref/rst/mathematics.html
.. _legacy_column_widths: docs/user/config.htmllegacy-column-widths

Links

• PyPI: https://pypi.org/project/docutils
• Changelog: https://pyup.io/changelogs/docutils/
• Homepage: http://docutils.sourceforge.net/