1. Mention multiplex as a dependency
2. Add ERB as a MIME-type

At least that works.

Closes #1788

Bumping them for every release just adds too much git
noise and history blowup.

Also moves handling of electricChars to readInput, removing
the timeout kludge.

Issue #2029

It may not provide these methods.

Closes #1051

And move closetag over to it.

This makes the code that gets the XML state out of the mode actually
sound and extensible.

Issue #820

Add CodeMirror.defineOption function for defining new options.

Add findMatchingBracket to the methods exported by this extension.

Closes #746

Since v2 is the canonical CodeMirror at this point