Closes #3922

Closes #3808

- more style classes: operator, builtin, meta, brackets
- literal metas (@ and ^^)
- many more operators
- mime type and extension from spec

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

UNION should be a keyword (like FILTER, et.al.) not an op

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

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.