Docx reader: Fix window path for image lookup.

Don't use os-sensitive "combine", since we always want the paths in our
zip-archive to use forward-slashes.
Docx reader: Modify mediabag test accordingly.
LaTeX template: Added \VerbatimFootnotes if there is verbatim in notes.

Fixes a bug when there is verbatim inside notes.
Closes #1616.
Updated tests for #1616 change.
Docx writer: Renumber header and footer relationships to avoid collisions.

We previously took the old relationship names of the headers and footer in
secptr. That led to collisions. We now make a map of availabl names in the
relationships file, and then rename in secptr.
ConTeXt writer: add function toLabel

This function can be used to sanitize reference labels so that
they do not contain any of the illegal characters \#[]",{}%()|= .

Currently only Links have their labels sanitized, because they
are the only Elements that use passed labels.
Bump text, random, http-client upper bounds
Merge pull request #1639 from RyanGlScott/master

Bump text, random, http-client upper bounds
MediaBag: Fixes Windows specific path problems

Changes the internal representation to fix the problem.

I haven't tested this on windows.

Closes #1597
Shared: Make collapseFilePath OS-agnostic
EPUB Tests: Seperating image testing from other features
HTML Writer: MathML now outputted with tex annotation.

Closes #1635
Add support for KaTeX HTML math

Closes #1626
Updated README to include information about KaTeX switches
HTML Writer: Don't double render when email-obfuscation=none

Closes #1625
HTML Reader: Recognise <br> tags inside <pre> blocks

Closes #1620
LaTeX template: load polyglossia before bibtex.

Fixes jgm/pandoc-templates#70.
Thanks to bluebirch.
Merge branch 'master' of github.com:jgm/pandoc
Org Reader: Parse multi-inline terms correctly in definition list

Closes #1649
Update tests for #1649