The `markdown` mode now supports styling overrides. The configuration
object passed to the class now accepts a `tokenTypeOverrides` object,
which allows the user to sepcify different CSS classes for elements.
This is useful for the case where the default CSS classes are reused
for multiple elements (e.g. `list1` maps to `variable-2` by default)
and more customized styling is desired.

Unit tests have been added to cover all types of styling overrides.

`A PKGBUILD is a shell script containing the build information required by Arch Linux packages.`
https://wiki.archlinux.org/index.php/PKGBUILD

So that both true and false highlight as atoms

Closes #3585

Issue #3601

- Previously, triple-quoted multi-line strings could be closed with a
  single quote, e.g. CodeMirror thought the following was a legal string
  literal: '''This string literal is not terminated correctly'.
  Also reported here: dart-lang/dart-pad#667
- String interpolation with $identifier and ${expression} now works

Closes #3596

Removed possible testing and unreachable code to avoid JavaScript
compiler errors:

...
codemirror/mode/coffeescript/coffeescript.js:271: WARNING - unreachable code
    if (false && current === ".") {
...

Closes #3558

support more arch/preamble/sections and fix clearing control flow
state.

* Removes like, ilike.
* Adds starts, ends, contains, toString, size, reverse.

Issue #3536

So that the xu/msgenny modes can be dynamically loaded from meta.js

Issue #3523

Issue #3496

Issue #3542

In C++14, the single-quote character may be used arbitrarily
as a digit separator in numeric literals.

Issue #3535

Damaged in 1a56b954

For proper syntax highlighting

Issue #3516