added NullMutex, extended Events so that mutex is a template param, minor performance optimzation for strategies

Foundation/include/Poco/NotificationStrategy.h

@@ -49,6 +49,9 @@ namespace Poco {
 template <class TArgs, class TDelegate> 
 class NotificationStrategy
 	/// The interface that all notification strategies must implement.
+	/// Note: Event is based on policy-driven design, so your strategy implementation
+	/// must offer all the methods from this interface (otherwise: compile errors)
+	/// but you don't need to extend from NotificationStrategy!
 {
 public:
 	NotificationStrategy()