AFNetworking notification's deprecated

The following notifications is deprecated in AFNetworking 2:

```obj-c
// AFURLSessionManager.m
//
AFNetworkingTaskDidStartNotification = @"com.alamofire.networking.task.resume";
AFNetworkingTaskDidFinishNotification = @"com.alamofire.networking.task.complete";
```
Probably this change generates impact for those using earlier versions of the Framework. 
I do not know if you intend to abandon support the previous version, create another branch or tag ...

If accepted, the podspec version has also been updated.