iOS 10的UICollectionViewDataSourcePrefetching方法

iOS 10的Tableview 和 CollectionView 出了一个新的DataSourcePrefetching代理。用于解决滑动时候的时候，让页面滑动的时候更加流畅。

应该是这样用的：

- (void)collectionView:(UICollectionView *)collectionView prefetchItemsAtIndexPaths:(NSArray *)indexPaths{
    
    for (NSIndexPath *indexPath in indexPaths) {
        if (indexPath.section == self.section && indexPath.item

- (void)collectionView:(UICollectionView *)collectionView cancelPrefetchingForItemsAtIndexPaths:(NSArray *)indexPaths{
    for (NSIndexPath *indexPath in indexPaths) {
        if (indexPath.section == self.section && indexPath.item