* markdown: Don't emit paragraph tags when a paragraph is "tight".
Motivation: Since the upgrade to remarkable.js (#3876), lists are rendered as
HTML like this:
```
<ul>
<li><p>One</p></li>
<li><p>Two</p></li>
<li><p>Three</p></li>
</ul>
```
The paragraph nodes insert blocks that break the visual flow of the list and are
unexpected e.g. compared to WikiText markup's rendering of a bulleted list.
Solution: remarkable.js annotates certain paragraph nodes as "tight", and in the
bulleted list case, the paragraph nodes wrapping the text of each list item are
marked tight.
remarkable uses the tight property to [elide paragraph tags in its
renderer](58b6945f20/lib/rules.js (L136-L142)).
This change implements the equivalent logic in TiddlyWiki's markdown rendering:
If a paragraph is marked tight, then we elide the `<p>` tag wrapping its children.
* Use ES5 Array.concat instead of ES6 spread operator.
* Add optional KaTeX support to the tiddlywiki/markdown plugin.
Uses the remarkable-katex plugin 1.1.8 by Brad Howes to enable KaTeX support if
the tiddlywiki/katex plugin is installed. Fixes#2984.
TESTED:
Created a test wiki with:
```
$ node tiddlywiki.js test --init markdowndemo
$ node tiddlywiki.js test --listen
```
* Verified markdown support works without the tiddlywiki/katex plugin enabled.
* Verified markdown support works with the tiddlywiki/katex plugin enabled.
* Verified KaTeX (both inline and blocks) work as expected when the
tiddlywiki/katex plugin is enabled.
* Mention remarkable-katex plugin usage in the readme Tiddler.
* Include the remarkable-katex license as a tiddler.
* Include the Remarkable license.
* Include unminified original source of remarkable-katex 1.1.8.
* Exploratory pass at adding support for macro params in filter operands
* whitspace correction
* rename varInfo to varTree for disambiguation
* Refactored parseMacroInvocation to be re-usable, performance improvements for variables with no params and tests
* Revised regular expression and removed spurious white space changes
* Revised regular expression and removed spurious white space changes
* More whitespace cleanup and added more tests for edge cases
* Added test for macro params with square brackets
* html-comment, that can be used in the pragma area
* add commentpragma test
* fix typo
* fix typo and change comments ab bit
* combine html-comment and pragma-comment and add some docs, how to use it
* Make docs simpler by removing caching info
* change h2 wording
* Make classic storyview work in new windows, too
* Make pop storyview work in new windows, too
* Make zoomin storyview insert and remove animation work in new windows, too
* Transclude widget: only refresh when transcluded text reference has changed, includes tests
* Refactor wiki.parseTextReference so it is re-usable for getting the parser info
* Re-arrange methods in wiki.js to improve diff readability
