Closes #4869

Issue #4868

Issue #4864

This is opt-in, the plugin needs to produce message_html instead of
message to be rendered as HTML.

This should help developers building this functionality out that may not
realize they need to source the linting library seperately.

Issue #3059

Closes #4855

Because the borders don't make much visual sense. And they cause dual
scroll bar issue when the editor takes 100% of page height.

You ca reproduce the issue here: http://mdp.tylingsoft.com/ Press
<kbd>CMD-,</kbd> to bring up the preferences panel and change the
theme to midnight.

[sublime keymap] "Add to selection" bindings (Ctrl-Alt-Up/Down on Windows, Cmd-Shift-Up/Down on Mac)

Also correct links to specification.

So that the addon doesn't try to put a single DOM node in two places

Closes #4848

Modern browsers handle updates to a textarea's value fast enough
to not do this anymore.

Issue #2703

Closes #4840

Issue #4839

Issue #4840

Closes #4839

Closes #4835