Asynchronous Request Creation

[jshier]

Perhaps the most inelegant bit of Alamofire's current API is the handling of multipart form uploads. Due to the asynchronous nature of the request creation, it doesn't support chaining like every other Request API, requiring users to get the actual upload request in the completion for the request creation. Alamofire should move to an asynchronous Request creation model for all request types. Not only could this greatly simplify multipart uploads, but would allow expensive operations in other requests as well, an issue we've had reported before. Most likely this will entail something like a Future API for Request, or at least an internal state machine so that method chaining can still work.

[jshier]

This was implemented in the rewrite.