Callbacks module extended

Now supports callback methods as well observer classes

levels example now uses callback methods

register,deregister now alias add/remove observer methods

minor version bump

lib/obsws/version.rb

@@ -7,11 +7,11 @@ module OBSWS
     end
 
     def minor
-      3
+      4
     end
 
     def patch
-      3
+      0
     end
 
     def to_a