Merge pull request #294 from Sondergaard/master

Register INotificationHandler as a collection

samples/MediatR.Examples.SimpleInjector/Program.cs

@@ -33,7 +33,7 @@ private static IMediator BuildMediator(WrappingWriter writer)
                 IncludeGenericTypeDefinitions = true,
                 IncludeComposites = false,
             });
-            container.Register(typeof(INotificationHandler<>), notificationHandlerTypes);
+            container.Collection.Register(typeof(INotificationHandler<>), notificationHandlerTypes);
 
             container.Register(() => (TextWriter)writer, Lifestyle.Singleton);