Connection and public channel subscription

Happy path websocket connection is now done, passing error and disconnection callbacks to the user now also works. Binding to either all or specific connection states is working.

Subscribing to public channels and receiving events is also now working. Binding to specific events is implemented.

Build now works correctly, and produces an executable jar that runs the Example application. Added a section to the readme that explains how to sync, develop and build the project.

Unsubscribe and unbind now also implemented.

Little bit of Javadoc on the Pusher class has been added.

Private channels and presence channels are finished.