Update docutils to 0.15.1

[pyup-bot]

This PR updates docutils from 0.13.1 to 0.15.1.

Changelog

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 (ko) mappings and latin.

* Several fixes to keep mor information on source in parsed elements,
isolate documents roles from other documents parsed, smartquotes, 
table gets width and latex table multicolumn cells, ...

0.14

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

* docutils/docs/ref/docutils.dtd:

- Enable validation of Docutils XML documents against the DTD:

* docutils/parsers/rst/:

- Added functionality: escaped whitespace in URI contexts.
- Consistent handling of all whitespace characters in inline markup
 recognition. (May break documents that relied on some whitespace
 characters (NBSP, ...) *not* to be recognized as whitespace.)

* docutils/utils/smartquotes.py:

- Update quote definitions for et, fi, fr, ro, sv, tr, uk.
- Add quote definitions for hr, hsb, hu, lv, sh, sl, sr.
- Differentiate apostrophe from closing single quote (if possible).
- Add command line interface for stand-alone use (requires 2.7).

* docutils/writers/_html_base:

- Provide default title in metadata.
- The MathJax CDN shut down on April 30, 2017. For security reasons, we
 don't use a third party public installation as default but warn
 if `math-output` is set to MathJax without specifying a URL.
 See math-output_ for details.

* docutils/writers/html4css1:

- Respect automatic table column sizing.

* docutils/writers/latex2e/__init__.py

- Handle class arguments for block-level elements by wrapping them
 in a "DUclass" environment. This replaces the special handling for
 "epigraph" and "topic" elements.

* docutils/writers/odf_odt:

- Language option sets ODF document's default language
- Image width, scale, ... set image size in generated ODF.

* tools/

- New front-end ``rst2html4.py``.

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 #124