Update undo implementation
Merge branch 'howling-mad-undo' into howling-mad

Conflicts:
	src/dom.js
Implement undo snapshot fallback
Use externs for publicly visible properties
Refactor undo
Remove obsolete exports
Add undo externs
Fix syntax error
Allow creation of stable range without arguments
Moves isControlCharacter()
Refactor naming
Refactor naming
Implement keypress character insertion
Implement editable context functions
Refactor traversing functions
Undoable text inserts
Clean up a little
Preserve range during undo
Refactor text insert undo
Implement composition of text insert changes