NEW +sendAsynchronousRequest:queue:completionHandler: If queue is nil, run handler immediately.

NEW: CPURLConnection -operation, CPError CPURLErrorDomain
CPURLConnection -operation gives access to the operation created with
the completionHandler: arg.
This allows to create dependencies between operations, setup priorities.
When the connection fails with a status code > 400 or is cancelled, the
operation is also cancelled and
the next operation is the queue is started.