* Implement ASCollectionGalleryLayoutDelegate
- It arranges items of the same size into a multi-line stack (say photo gallery or pager). It takes advantage of the fact that its items always have a fixed size to measure as few items as possible while still being able to track their positions at all time. This helps reduce startup/reloadData time, as well as memory footprint.
- It then uses a measure range, which also works as a allocate range, to figure out which items to measure ahead of time. And it guarantees that each item is scheduled to measure only once.
- Lastly, ASCollectionLayoutDelegate has some new methods that allow delegates to hook up and stay ahead of layout attributes requests from the backing view. ASCollectionGalleryLayoutDelegate for example uses these methods to ensure elements that have their layout attributes requested are always ready for consumption, and to measure more elements in the background.
* Handle items that span multiple pages and other improvements in gallery delegate
* Minor fixes
* Fix failing tests
* Fix custom collection example
* Implement missing method in gallery layout delegate
* Fix warnings
* Some improvements
- Collection layout delegates must have a crollable directions property.
- Simplify gallery delegate by not storing unmeasured attributes since calling measure on already measured elements should be cache hits and super fast.
- Abstact some code in gallery delegate to ASCollectionLayoutState+Private and _ASCollectionGalleryLayoutItem.
- Other improvements in gallery delegate
* Fix file licenses
* Move measure range logic to ASCollectionLayout
* Track unmeasured elements
* Remove pending layout in ASCollectionLayout
* Get back pending layout because the timing to latch new data is not ideal
* Add ASCollectionLayoutCache
* Fix file licenses
* Fix xcodeproj
* Add async collection layout to examples/ASCollectionView
* Measure method in ASCollectionLayout to be a class method
* Encourage more immutable states
- Make -calculateLayoutWithContext: to be class methods in ASDataControllerLayoutDelegate and ASCollectionLayoutDelegate.
- Add layout delegate class and layout cache to ASCollectionLayoutContext+Private, to be use by ASCollectionLayout only.
- ASDataController no longer allocates all nodes but lets ASCollectionLayout determine.
- Add scrollableDirections to the layout context since it's often needed by the layout pass. Otherwise users have to wrap it in an info object.
- Update built-in layout delegates and CustomCollectionView example.
- Publish ASHashing. It might be helpful for clients that implement custom collection info objects.
* Remove additionalInfo property in ASCollectionLayoutState
* ASCollectionLayoutState to correctly filter unmeasured elements
* Add ASHashing to umbrella header
* Fix file licenses
* Add ASDispatchAsync and use it in ASCollectionLayout
* Improve code comment in ASCollectionLayoutState
