Update for AFNetworking 2.0
Fix Xcode 6 build error
Refactor to use default HTTP headers
Rename AFOAuth2Client to AFOAuth2RequestOperationManager
Add AFOAuth2RequestSerializer

For authenticating requests in separate pipelines
Change the path argument to URLString
Document AFOAuth2RequestSerializer
Remove AFOAuth2RequestSerializer
Fixing documentation parameter names
Adding __unused annotations
Replacing string literals with NSStringFromSelector @selector for NSCoding
Removing conditional compilation for Security framework features
Adding copy to value type property declarations
Removing explicit property synthesis
Adding missing braces for if statements
Changing == nil check to !
Refactoring AFKeychainQueryDictionaryWithIdentifier
Refactoring to use NSDictionary literals

Adding NSParameterAsserts
Refactoring to use object subscripting
Implementing AFErrorFromRFC6749Section5_2Error