Created ASCollectionNode with new example project.

Eases support for nesting horizontally scrolling elements within a vertical scroller.

Further changes will improve the API, and optimize handling of the nested working ranges.

examples/HorizontalWithinVerticalScrolling/Sample/HorizontalScrollCellNode.h

@@ -0,0 +1,22 @@
+/* This file provided by Facebook is for non-commercial testing and evaluation
+ * purposes only.  Facebook reserves all rights not expressly granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#import <AsyncDisplayKit/AsyncDisplayKit.h>
+
+/**
+ * This ASCellNode contains an ASCollectionNode.  It intelligently interacts with a containing ASCollectionView or ASTableView,
+ * to preload and clean up contents as the user scrolls around both vertically and horizontally — in a way that minimizes memory usage.
+ */
+@interface HorizontalScrollCellNode : ASCellNode <ASCollectionViewDelegate, ASCollectionViewDataSource>
+
+- (instancetype)initWithElementSize:(CGSize)size;
+
+@end