Timeouts are now modifyable in the JavaNetURLConnectionManager class

Hi, I've added the possibility to change the timeouts for the HttpURLConnection, which is useful for big exports with an app running on Google AppEngine.

Thanks for this great lib, it would be even better if you specified in the documentation the existence of JavaNetURLConnectionManager as an alternative to HttpClientConnectionManager for people who can't use things from the apache package, when running Java on AppEngine for instance.