The attached Listeners are notified of the following events:
sent before a HTTP request that is not a result of previous redirect.
sent upon receiving a successfull 2xx response (or 3xx response, if it is not a redirect or if redirect processing is disabled).
sent when a 3xx redirection response is received, before following a redirect
sent on 4xx, 5xx response
the Listener will be attached to the created HTTP_Request
objects and will be notified of their events as well.