Implement ASCollectionView. Horizontal scrolling is not supported yet.
Fix ASCollectionView::rangeControllerVisibleNodeIndexPaths: to return a sorted array.
Provide ASCollectionView::calculatedSizeForNodeAtIndexPath:, to be used in custom UICollectionViewLayouts.
Make constrained size for nodes adapt to ASCollectionView's scrolling direction.
Update ASRangeController to support ASCollectionView and no longer assume vertical scrolling when calculates working range.
Add CollectionViewSample.

Update sample for more items.