Release 5.20.0

### Bug fixes

Make `newlineAndIndent` command work with multiple cursors on the same line.

Make sure keypress events for backspace are ignored.

Tokens styled with overlays no longer get a nonsense `cm-cm-overlay` class.

Line endings for pasted content are now normalized to the editor's [preferred ending](http://codemirror.net/doc/manual.html#option_lineSeparator).

[javascript mode](http://codemirror.net/mode/javascript): Improve support for class expressions. Support TypeScript optional class properties, the `abstract` keyword, and return type declarations for arrow functions.

[css mode](http://codemirror.net/mode/css): Fix highlighting of mixed-case keywords.

[closebrackets addon](http://codemirror.net/doc/manual.html#addon_closebrackets): Improve behavior when typing a quote before a string.

### New features

The core is now maintained as a number of small files, using ES6 syntax and modules, under the `src/` directory. A git checkout no longer contains a working `codemirror.js` until you `npm build` (but when installing from NPM, it is included).

The [`refresh`](http://codemirror.net/doc/manual.html#event_refresh) event is now documented and stable.
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