• Breaking Change Renamed cancelled in the Cancellable protocol to isCancelled.
• Breaking Change Renamed URL in Endpoint to url.
• Breaking Change Renamed StructTarget to MultiTarget.
• Demo project has been updated with new DemoMultiTarget target, new project
  structure and more.
• Readded support for iOS 8 and macOS 10.10.
• Added validate option in TargetType, to allow enabling Alamofire automatic validation on requests.
• Added mapString(atKeyPath:) to Response, SignalProducerProtocol, and ObservableType.