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.

AsyncDisplayKit/ASCollectionView.mm

@@ -137,6 +137,11 @@ static BOOL _isInterceptedSelector(SEL sel)
 #pragma mark -
 #pragma mark Lifecycle.
 
+- (instancetype)initWithCollectionViewLayout:(UICollectionViewLayout *)layout
+{
+  return [self initWithFrame:CGRectZero collectionViewLayout:layout asyncDataFetching:NO];
+}
+
 - (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout
 {
   return [self initWithFrame:frame collectionViewLayout:layout asyncDataFetching:NO];
@@ -175,6 +180,8 @@ static BOOL _isInterceptedSelector(SEL sel)
 
   _maxSizeForNodesConstrainedSize = self.bounds.size;
   
+  self.backgroundColor = [UIColor whiteColor];
+  
   [self registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"_ASCollectionViewCell"];
   
   return self;