Added a separate queue for notifications that need to be re-sent.
Swapped the order of queue reads so we drain the retry queue before trying to send new notifications.
Merge branch 'master' into separate_retry_queue

Conflicts:
	src/main/java/com/relayrides/pushy/apns/ApnsClientThread.java
	src/main/java/com/relayrides/pushy/apns/PushManager.java
Added the beginnings of a PushManagerFactory.
Removed public `enqueuePushNotification` methods.
Documented new classes/methods and updated the examples in the README.
Return unsent messages from the retry queue, too.
Used more direct contact information in an author tag.
Added a note about the lingering GlobalEventExecutor thread (closes #29).
Added a link to the mailing list.
Switched to strong references for registered listeners.
Throw an IllegalStateException when registering a listener for an already-shut-down PushManager.
Merge pull request #40 from relayrides/strong_listener_references

Use strong references instead of weak references for rejected notification listeners
Merge branch 'master' of github.com:relayrides/pushy into separate_retry_queue

Conflicts:
	src/main/java/com/relayrides/pushy/apns/PushManager.java
Merge pull request #38 from relayrides/separate_retry_queue

Separate retry queue (fixes #20)
Move clientThreads back to list. Add test for replace thread.
Fixed a minor typo in a comment.
Broaden generic param of rejectedNotificationListener
Merge pull request #34 from robertclancy/broaden-generic-type

Broaden generic param of rejectedNotificationListener
Fix whitespace for thread death test.