Add the podspec to xcode project so that it could be updated easily.
[FIX] stop the activity indicator when set the image through setImage: directly.
[FIX] implement the isImageLoading method.
[FIX] do not start if the image is loading.
Post the will / did load image notifications.
Make the isImageLoaded variable public and readonly.
[FIX] add edge case when setting nil.
Add documentation.