Fix inaccurate type info in docs

Closes #1459
[clojure mode] Fix allowed symbol characters

Closes #1460
[lint addon] Don't try to display tooltip above top of document
[lint addon] Make sure tooltips are always hidden when their ref node is removed
show-hint addon to emit "hintShowed" and "hintClosed" events
[show-hint addon] Use events to notify hint source on open/close/select

Issue #1454
Document addToHistory option to markText
Mark release 3.12
Bump version number post-3.12
More !@# selection drawing work.
Merge branch 'master' of https://github.com/marijnh/CodeMirror
Ok, making some good progress finally on making sense of collapsed lines with different text indents and paddings.