[Issue #1205] Initial implementation of change to single response serializer
Implementing AFCompoundSerializer
Using compound serializer by default with AFHTTPClientgs
Removing _AFNETWORKING_ALLOW_INVALID_SSL_CERTIFICATES_ backwards compatibility
Executing passed success/failure blocks in content type operations
Merge branch '2.0-single-response-serializer' into 2.0
Merge branch '2.0' of github.com:AFNetworking/AFNetworking into 2.0