NSURLDownload class downloads a request asynchronously and saves the data to a file. The interface for
NSURLDownload provides methods to initialize a download, set the destination path and cancel loading the request.
The delegate object assigned to each instance of this class should implement the methods defined by the
NSURLDownload protocol. These methods provide the delegate with the current status of in-progress asynchronous downloads and allow the delegate to customize the URL loading process. These delegate methods are called on the thread that started the asynchronous load operation for the associated