improve rotation and scrollToItem
improve rotation and scrollToItem

jianwoo/PSTCollectionView,CorzFree/PSTCollectionView,niuxinghua/PSTCollectionView,steipete/PSTCollectionView,godLoveLucifer/PSTCollectionView,Anish-kumar-dev/PSTCollectionView,ba01ei/PSTImprovedCollectionView,zace-yuan/PSTCollectionView,StephaneDelcroix/PSTCollectionView,zjh171/PSTCollectionView,Kevin775263419/PSTCollectionView,Amnysia/PSTCollectionView,StephaneDelcroix/PSTCollectionView,thevuuranusls/PSTCollectionView