Add helper function Cmd.ofAsyncResult

[TimLariviere]

Cmd.ofAsyncResult is useful when dealing with API calls

module Server =
    let getDataAsync () =
        async {
                let! response = ...

                if response.StatusCode = Unauthorized then
                     return Error "Unauthorized"
                else
                     return Ok response.Data
        }

Cmd.ofAsyncResult
     Server.getDataAsync
     (fun data -> DataRetrievedSuccessfully data)
     (fun error -> DataRetrievalError error)
     (fun ex -> DataRetrievalFailure ex)