Merge tag 'v0.19.1' into develop

0.19.1
Fixed an error in the branch check.
Added features to onbeforeunload.

onbeforeunload now accepts registering arbitrary checks to decide
whether to show a prompt. Wed sets it so that the prompt is not shown
if the document is saved.
Added support for localstorage file storing.
Serialization fix for IE.
Updated the changelog to the real changes.
Updated version information.
Version bump.
Relaxed caret position check.

This check kept failing on OS X due to a rounding error.
Adjustments to what is supported.
Added a flag to allow building gh-pages-build.

Allows building it even if not in master branch.
Many various doc updates.
Dependencies update.
More todo.
Added a bit of documentation about releasing.
Merge branch 'release/0.20.0'