Ref #16. Send multiple frames at onece
added feedback proxy feature

* The current implementation of this feature stores full list of device tokens to server memory and dump it as response. We should change do that as streaming for large feedback list
* Change the internal APNSProxyServer.app_config format from list to dict (settings['APPLICATIONS'] is not changed)
Add tests
Fix pep8 issues
Resolve "Test fails on Python 2.6"
Merge pull request #21 from voyagegroup/feedback-proxy

added feedback proxy feature
Refactoring
Add tests
Update README.md
Fix log
Merge pull request #20 from voyagegroup/send_at_once_multiple_frames

Send multiple frames at once