Closes #4345

To avoid false positives.

Closes #3752

Closes #3365

Closes #2724

Closes #2692

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

relates to https://github.com/marijnh/CodeMirror/issues/314

relates to https://github.com/marijnh/CodeMirror/issues/314

Closes #2146

Moving to a situation where there's only one LICENSE for the whole
distribution.

Issue #1701

* Handle default string % literal for Ruby

  %{Hello World} == %q{Hello World}

  One gotcha though:

  5%(2) == 5 % 2

  Will be seen as a string, but it will be interpreted
  as the modulo operator by ruby.

* Variables names can't include a ? nor a !

* Improve symbols parsing rules

  - can be operators (e.g :+, :/, :-, :>>)
  - start with @ or $
  - end with !, ? or =
  - can't start by a digit

  Though when defined in reverse as hash keys (e.g {foo: 'bar'})

  - can only start with [a-zA-Z\_]
  - can't end with =

* Instance and class variables can't start by a digit but globals can be only digits

* Add some missing keywords

  Actually only __END__ is really a keyword.
  But __FILE__, __LINE__ and __dir__ are special variables so most editors highlight them as keywords.

* Several regexp improvements

  - Use the string-2 class for regexps like JS mode
  - Xonsider %r as a regexp
  - Handle interpolation inside regexps

  It allow to colorize properly stuffs like:

  ```ruby
/foo #{1 + 2}/
%r{foo #{@bar} baz}
```

* Fix parsing of brace enclosed string literals with interpolation

  As an example:

  ```ruby
%Q{foo #{42} baz #{26} fizz}
```
  The coloration was broken after the first interpolation.

Closes #1133

As spotted by the extended linter.

Add CodeMirror.defineOption function for defining new options.

Add findMatchingBracket to the methods exported by this extension.

Closes #746

Closes #560

This isn't really correct, but covers most cases. Someone with more
knowledge of Ruby's syntax will have to chime in what the real
solution would look like.

Issue #314

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.