Issue #2360

Issue #2360

Closes #1252

They are triggered at points where the editor is in an inconsistent state,
so if their handlers cause further action on the editor/doc, bad things
will happen.

This helps performance on v8 (in microbenchmarks) and is less noisy.

Regular literals are still accepted, the constructor is only used to create
objects, doesn't attach any methods.

Issue #1194

Add test.

 - Move a lot of methods from the CodeMirror to the Doc prototype
 - Allow getting, attaching, and copying of Doc objects
 - Add linkedDoc to create documents that stay in sync
 - Allow such linked docs to be sub-view on their parent
 - Rewrite history handling
 - Remove the concept of a view

Documentation still failing.