Added isSignalExists(ulong id) to check whether a signal handler exists for a given event id

source/eventy/engine.d

@@ -348,6 +348,15 @@ public final class Engine : Thread
         return matchedHandlers;
     }
 
+    /**
+    * Checks if there is a Signal that handles the given
+    * event ID
+    */
+    public bool isSignalExists(ulong id)
+    {
+    	return getSignalsForEvent(new Event(id)).length != 0;
+    }
+
     /**
     * push(Event e)
     *