Add Apple JWT Token based authentication (sideshow#43)

* Add Apple JWT Token based authentication
* Add JWT token auth docs

Add CloseIdleConnections method to close tcp connections (sideshow#92)

Add TCP Keepalive (sideshow#90)

Move to vendored dependencies (sideshow#86)

* Add vendored dependencies
* Update README install instructions

Merge pull request sideshow#81 from sideshow/feature-context

Feature request context

Add PushKit/VoIP support note to README

Closes sideshow#71

Add iOS Support

Update README.md

APNS/2 0.5