Add LCS diffing support to NSArray

AsyncDisplayKit/Private/NSArray+Diffing.h

@@ -0,0 +1,18 @@
+//
+//  NSArray+Diffing.h
+//  AsyncDisplayKit
+//
+//  Created by Levi McCallum on 1/29/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface NSArray (Diffing)
+
+/**
+ * Uses a bottom-up memoized longest common subsequence solution to identify differences. Runs in O(mn) complexity.
+ */
+- (void)asdk_diffWithArray:(NSArray *)array insertions:(NSMutableIndexSet **)insertions deletions:(NSMutableIndexSet **)deletions;
+
+@end