* Make our async deallocation functions take a double pointer, so we can be sure we've released before the queue drains
* Make it a class property
* Fix the return type
* Use a locker
* Improve release notes
* Small changes required by the layout debugger
- `ASDisplayNode` can be told to not flatten its layout immediately but later on. The unflattened layout is also stored in a separate property. It's needed for inspecting not only display nodes but also layout specs used to compute a layout tree.
- `ASLayout` can be told to always retain its sublayout elements. This is needed especially for layout specs since they are usually not retained after an ASLayout was computed.
* Update CHANGELOG
* Address comments
