Release 3.1

[Marijn Haverbeke]

This is a 'big' release, with a lot of changed code. The interface is
almost entirely backwards-compatible, but upgrade with some care,
since new code always carries the risk of breaking some specific use
case.

Main changes:

- *Incompatible*: key handlers may now _return_, rather than _throw_
CodeMirror.Pass to signal they didn't handle the key.
- Make documents a first-class construct, support split views and
subviews.
- Add a new module for showing completion hints. Deprecate
simple-hint.js.
- Extend htmlmixed mode to allow custom handling of script types.
- Support an insertLeft option to setBookmark.
- Add an eachLine method to iterate over a document.
- New addon modules: selection marking, linting, and automatic bracket
closing.
- Add "beforeChange" and"beforeSelectionChange" events.
- Add "hide" and "unhide" events to marked ranges.
- Fix coordsChar's interpretation of its argument to match the
documentation.
- New modes: Turtle and Q.
- Further improvements to the vim mode.

Enjoy! Download from http://codemirror.net/codemirror-3.1.zip

Note: github seems to have a problem where it associates the v3.1 tag
with a completely incorrect commit, so right now the 'full list of
patches' link on the website is broken, and if you fetch tag v3.1 from
github, you won't get the correct code.

Best,
Marijn