Issue #4868

Issue #4188

Doesn't show states (but shouldn't crash) on old browsers.

It is turning into a major headache, since apparently a
lot of modes are written with the assumption that empty
tokens are okay.

Closes #2517

Issue #2447

All tests now check whether indentation from mode corresponds
to the indentation in the test source. test.indentation is
gone.

Closes #1696

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

- 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

Markdown mode

- Add additional link tests and correctly match link titles on next
  line.

- Adjust tests code so sections (including "Basics") can be rearranged
  and removed easily without breaking the script.

- Add tests and fix highlighting for lists.

Test harness

- Sort styles in mode test script so "quote string" = "string quote".

(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".