Update docutils to 0.16

[pyup-bot]

This PR updates docutils from 0.14 to 0.16.

Changelog

0.16

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

.. Note::

Docutils 0.15.x is the last version supporting Python 2.6, 3.3 and 3.4.

Docutils 0.16.x supports Python 2.7 and Python >= 3.5 natively,
without the use of the ``2to3`` tool.

* reStructuredText:

- Keep `backslash escapes`__ in the document tree. This allows, e.g.,
 escaping of author-separators in `bibliographic fields`__.

__ http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.htmlescaping-mechanism
__ docs/ref/rst/restructuredtext.htmlbibliographic-fields

* LaTeX writer:

- Informal titles of type "rubric" default to bold-italic and left aligned.
- Deprecate ``\docutilsrole`` prefix for styling commands:
 use ``\DUrole`` instead.
- Fix topic subtitle.
- Add "latex writers" to the `config_section_dependencies`.
- Ignore classes for `rubric` elements
 (class wrapper interferes with LaTeX formatting).

* tools/buildhtml.py

- New option "--html-writer" allows to select "html__" (default),
 "html4" or "html5".

__ html: docs/user/html.htmlhtml

* docutils/io.py

- Remove the `handle_io_errors` option from io.FileInput/Output.

* docutils/nodes.py

- If `auto_id_prefix`_ ends with "%", this is replaced with the tag name.

.. _auto_id_prefix: docs/user/config.htmlauto-id-prefix

* Various bugfixes and improvements (see HISTORY_).

0.15

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

.. Note::

Docutils 0.14.x is the last version supporting Python 2.4, 2.5,
3.1, and 3.2.

Docutils 0.15.x is compatible with Python versions 2.6, 2.7 and 3.3 to 3.5
(cf. `Python 3 compatibility`_).

* reStructuredText:

- Allow embedded colons in field list field names (before, tokens like
 ``:this:example:`` were considered ordinary text).

- Fixed a bug with the "trim" options of the "unicode" directive.

* languages: Added Korean localisation (ko).

* Bugfixes (see HISTORY_).

Links

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

[pyup-bot]

Closing this in favor of #823