Mentioning that the unregister method also cleans up event handlers on the docs.

Added detail about requiring no extension as the file name.

Work on silent push
Handle content-available key
Add completionHandler
Implement JS
Send plugin result from finish
Document background push
Android shim for finish method

Remove gcm.jar
Implement GCM Clould Messaging
Implement Token Refresh Listener
Update Android compilation instructions

Being explicit about possible types/values on ios options: booleans can be passed as strings.
fixes #180

add error handling