HTML reader:  Parse LaTeX math if appropriate options are set.

* Moved inlineMath, displayMath from Markdown reader to Parsing.
* Export them from Parsing.  (API change.)
* Generalize their types.
Text.Pandoc:  Don't default to pandocExtensions for all writers.

In particular, we don't want to default to math parsing for the
HTML writer.
Small change to HTML reader tests.

"$" is now a special character.
Documented use of extensions with non-markdown input formats.
Updated changelog.
More changes to github-upload.sh.  Still doesn't work, though.
Markdown reader: Fixed bug with literal `</div>` in lists.

Closes #1078.
Small performance improvement in list parsing.
Another small performance improvement.
OSX package:  Create .zip rather than .dmg.
Version mubp to 1.12.2.1
Updated changelog.
Updated beamer template for booktabs.
Don't use tilde code blocks with braced attributes in gfm output.

A consequence of this change is that the backtick form will be
preferred in general if both are enabled.  I think that is good,
as it is much more widespread than the tilde form.

Closes #1084.
Relaxed version bounds for array, http-conduit, process.
Added `withSocketsDo` around http conduit code in `openURL`.

This should address #1080, but further testing on Windows is needed
before we can close the bug.
Allow zip-archive 0.2.
Fixed documentation bug.
Added more explanation of metadata in README.
default latex template:  added abstract variable.