Text.Pandoc.Writer.Shared: fixed bug in tagWithAttrs.

A space was omitted before key-value attributes, leading
to invalid HTML.
Slides:  Preserve `<div class="references">` in references slide.
Markdown reader:  Yaml block must start immediately after `---`.

If there's a blank line after `---`, we interpreted it as
a horizontal rule.
TexMath: Export readTeXMath', which attends to display/inline.

Deprecate readTeXMath, and use readTeXMath' in all the writers.
Require texmath >= 0.6.5.
HTML reader:  Use pandoc Div and Span for raw "<div>", "<span>".

Only if --parse-raw.
Markdown reader: Correctly handle empty bullet list items.

For example:

    - one
    -
    - two

This should NOT be parsed as a setext header followed by a list.
Version bump to 1.12.2.
Don't print `<span>` tags in 'plain' output.
Require texmath >= 0.6.5.2.
Docx writer:  Fix URL for core-properties in `_rels/.rels`.

Partially addresses #1046.
Docx writer: fixed core metadata.

- Don't create empty date nodes if no date given.
- Don't create multiple dc:creator nodes; instead separate by
  semicolons.

Closes #1046.
recognize svg tag in HTML Reader

avoids adding lots of `<p>` tags in embedded SVG content,
for instance in markdown to HTML.
Merge pull request #1048 from minrk/svg

recognize svg tag in HTML Reader