v1.4.0

Renamed nextToUndo/Redo to nextUndo/Redo. The earlier naming has been deprecated and will be removed in the next release.

Added a configuration option: UndoManager can preventMerge after a period of inactivity from the change stream. For example, if a user types "apple" into some area, pauses for a second, and then writes "oranges", there should not be a single change that inserts "appleorange" but two changes: one that inserts "apple" and one that inserts "orange"