Update documentation for diff

Summary:
Update documentation for diff to be in sync with ab890fc. Documentation update only, nothing to test.

- [x] All tests pass. Demo project builds and runs.
- [x] I added tests, an experiment, or detailed why my change isn't tested.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Closes #231

Differential Revision: D4211422

Pulled By: rnystrom

fbshipit-source-id: 9cb637e42300d9db173d99c1305845984d52ce7b

README.md

@@ -129,7 +129,7 @@ You can return an array of _any_ type of data, as long as it conforms to `IGList
 
 `IGListKit` uses an algorithm adapted from a paper titled [A technique for isolating differences between files](http://dl.acm.org/citation.cfm?id=359467&dl=ACM&coll=DL) by Paul Heckel. This algorithm uses a technique known as the *longest common subsequence* to find a minimal diff between collections in linear time `O(n)`. It finds all **inserts**, **deletes**, **updates**, and **moves** between arrays of data.
 
-To add custom, diffable models, you need to conform to the `IGListDiffable` protocol and implement `diffIdentifier()` and `isEqual(_:)`.
+To add custom, diffable models, you need to conform to the `IGListDiffable` protocol and implement `diffIdentifier()` and `isEqual(toDiffableObject:)`.
 
 For an example, consider the following model:
 
@@ -165,7 +165,7 @@ extension User: IGListDiffable {
     return primaryKey
   }
 
-  func isEqual(object: Any?) -> Bool {
+  func isEqual(toDiffableObject object: Any?) -> Bool {
     if let object = object as? User {
       return name == object.name
     }
@@ -176,7 +176,7 @@ extension User: IGListDiffable {
 
 The algorithm will skip updating two `User` objects that have the same `primaryKey` and `name`, even if they are different instances! You now avoid unecessary UI updates in the collection view even when providing new instances.
 
-> **Note:** Remember that `isEqual(_:)` should return `false` when you want to reload the cells in the corresponding section controller.
+> **Note:** Remember that `isEqual(toDiffableObject:)` should return `false` when you want to reload the cells in the corresponding section controller.
 
 ### Diffing outside of IGListKit
 

Source/IGListDiff.h

@@ -24,7 +24,7 @@ typedef NS_ENUM(NSInteger, IGListDiffOption) {
      */
     IGListDiffPointerPersonality,
     /**
-     Compare objects using `-[NSObject isEqual:]`.
+     Compare objects using `-[NSObject isEqualToDiffableObject:]`.
      */
     IGListDiffEquality
 };
@@ -38,7 +38,7 @@ typedef NS_ENUM(NSInteger, IGListDiffOption) {
 
  @return A result object containing affected indexes.
  */
-FOUNDATION_EXTERN IGListIndexSetResult *IGListDiff(NSArray<id<IGListDiffable> > *_Nullable oldArray,
+FOUNDATION_EXTERN IGListIndexSetResult *IGListDiff(NSArray<id<IGListDiffable>> *_Nullable oldArray,
                                                    NSArray<id<IGListDiffable>> *_Nullable newArray,
                                                    IGListDiffOption option);
 

Source/IGListDiff.mm

@@ -135,7 +135,7 @@ static id IGListDiffing(BOOL returnIndexPaths,
                     }
                     break;
                 case IGListDiffEquality:
-                    // use -[IGListDiffable isEqual:] between both version of data to see if anything has changed
+                    // use -[IGListDiffable isEqualToDiffableObject:] between both version of data to see if anything has changed
                     // skip the equality check if both indexes point to the same object
                     if (n != o && ![n isEqualToDiffableObject:o]) {
                         entry->updated = YES;