Issue #2928
Issue #2958

This prevents a stray $ from setting the whole rest of
the document to math mode.

Closes #2928

Closes #2851

Bumping them for every release just adds too much git
noise and history blowup.

Tests are now specified in a less redundant format, and should be
easier to read and write.

As spotted by the extended linter.

- Integrated stex and Markdown mode tests into main test harness

- Added ability to restart tests partway through

- Added verbose option, to add message to output for *every* test

- Added ability to show verbose messages and run specific tests or all tests for 1+ mode(s) via location.hash

- Added support for custom messages (either return value [pass] or throw value [fail])

- Switched away from .innerHTML, .write(), etc in most places

- Make the progress bar actually 0px wide when 0% complete (and still keep padding)

- Added link to tests from each mode's demo page

(Squashed commit. Below are the original commit messages:)

- Add highlighting test for Markdown for consecutive backticks.

- Make it possible to wrap inline code in multiple backticks.

- Add highlighting test for Markdown mode to only allow a single space
  to separate brackets.

- Make it possible to separate bracket groups with a space.

- Allow for horizontal rules to use dashes.

- Allow for *any* number of -'s or ='s for setex headers.

- Remove requirement that the text for setext headers have to be
  highlighted.

- Might revisit someday to work on this, but in the meantime, it's
  better to prevent regressions than to be picky about what would be
  highlighted in an ideal world.

- Correctly match single line footnotes with title.

- Match inline links in Markdown mode.

- Don't match unclosed code blocks.

- Get mode test highlighter in line with CodeMirror.highlight().

- It would be nice to use all native functions, to avoid having to update this manually each time.

- Fix tests per fixes made to mode test highlighter.

- Properly handle multiple classes for mode tests.

- More correct handling of EM and STRONG in Markdown mode.

  Per Markdown documentation: "You can use whichever style you prefer;
  the lone restriction is that the same character must be used to open
  and close an emphasis span." # This is the 15th commit message:

- Allow escaping of * and _ by surrounding with spaces.

  Per Markdown documentation:

  "But if you surround an * or _ with spaces, it’ll be treated as a
  literal asterisk or underscore."

- More correct support for inline code blocks.

- Adjust Markdown highlighting tests to fit readability, rather than
  100% conformance with Markdown documentation.

  Although unclosed italics, bold, and inline code would not be
  formatted by a Markdown parser, it is extremely helpful to have the
  styles added even when it is not yet closed. It may be a good idea
  to add an 'incomplete' flag for each at some point, in order to
  style it (and mark it) as different. Perhaps piggyback off of
  "error".

Since v2 is the canonical CodeMirror at this point

So that I can put other doc-related stuff there without polluting the
root dir.

It's tiny anyway, no need to force people to include yet another file.

This normalizes the classes used by most of the modes
(reStructuredText and diff didn't fit in), and makes them all
reference a central style sheet (under theme/). It also adds a theme
option that can be set to change the theme, and defines a few
different themes (some based on old mode colors).

- Trailing commas in object literals are not allowed by the spec
  and are handled poorly in some browsers.
- Added var to some variable declarations that were not meant to be globals.