Adds _getNestedView to Layout and Collection Views.
Refactor Application to subclass Object
Refactor Behavior to subclass Object
Refactor Region to sub-class Object
Removes IIFE patterns in source.
Removes slice from jshintrc
Adds deprecation notice regarding Callbacks.
Add JSDOC Preview
Minor: simplify RegionManager emptyRegions
Avoid computing path when no onRoute set
Minor: attempt to avoid _.result call in normalizeKeys
Use reduce in View.configureTriggers
Use rest in Module.create
UndelgateEvents: use apply with arguments instead of slice
Use _.invoke in Module.stop
Minor: use _.rest in View.serializeModel and ItemView.serializeCollection
Optimization refactor of triggerMethodOn
Fix typos in Controller.yaml file
Allow non-DOM-backed regions with `allowMissingEl`

* `allowMissingEl` option is respected by `_ensureElement`
* `_ensureElement` returns boolean, indicating whether or not element is available
* `Region#show` early-terminates on missing element
* Increase jshint maxstatements allotment for `Region#show`
Document deprecation of Marionette.Deferred for #1982

Unless additional configuration is added in v3, this file can be
removed.