Release 1.1.5 - Events + Detailed Campaign Data

This release changes the way Events (previously called Notifications)
are communicated from the SDK. Previously NSNotification observers were
used, now subscribe/unsubscribe methods have been created to listen for
these events. It aims to make it easier to listen to events and give
more control in subscribing/unsubscribing.

Detailed campaign data access has been also been added. A new
"campaign" method where you pass it a notification dictionary and it
fetches detailed data from the API such as the newly added "meta" json
field in the "Advanced Fields" section of the campaign creation admin
console. The reason for this is that push notifications can only send
256 bytes, so for larger payloads this API call is necessary.

README and example application have been updated to reflect these
changes.