mixin Callback module

observers should now be registered directly onto vm object

example updated to reflect changes

examples/events/main.rb

@@ -3,7 +3,7 @@ require_relative "../../lib/voicemeeter"
 class Main
   def initialize(vm)
     @vm = vm
-    @vm.callback.register(method(:on_pdirty), method(:on_mdirty), method(:on_midi), method(:on_ldirty))
+    @vm.register(method(:on_pdirty), method(:on_mdirty), method(:on_midi), method(:on_ldirty))
   end
 
   def run

examples/midi/main.rb

@@ -5,7 +5,7 @@ class Main
 
   def initialize(vm)
     @vm = vm
-    @vm.callback.register(self)
+    @vm.register(self)
   end
 
   def run