Add HeaderDoc to DCPathItemButton.h.

DCPathButton/Classes/DCPathItemButton.h

@@ -10,17 +10,42 @@
 
 @class DCPathItemButton;
 
+/*!
+ *  `DCPathItemButtonDelegate` protocol defines method that informs the delegate object the event of item button's selection.
+ */
 @protocol DCPathItemButtonDelegate <NSObject>
 
+/*!
+ *  Tells the delegate that the `DCPathItemButton` has been selected.
+ *
+ *  @param itemButton A `DCPathItemButton` that has been selected.
+ */
 - (void)itemButtonTapped:(DCPathItemButton *)itemButton;
 
 @end
 
 @interface DCPathItemButton : UIButton
 
+/*!
+ *  The location of the `DCPathItemButton` object in a `DCPathButton` object.
+ */
 @property (assign, nonatomic) NSUInteger index;
+
+/*!
+ *  The object that acts as the delegate of the `DCPathItemButton` object.
+ */
 @property (weak, nonatomic) id<DCPathItemButtonDelegate> delegate;
 
+/*!
+ *  Creates a `DCPathItemButton` with normal and highlighted foreground and background images of the button.
+ *
+ *  @param image                      The normal foreground image.
+ *  @param highlightedImage           The highlighted foreground image.
+ *  @param backgroundImage            The normal background image.
+ *  @param backgroundHighlightedImage The highlighted background image.
+ *
+ *  @return A `DCPathItemButton` object.
+ */
 - (instancetype)initWithImage:(UIImage *)image
              highlightedImage:(UIImage *)highlightedImage
               backgroundImage:(UIImage *)backgroundImage