Allow for calling handlers from JS with just a handler name and respo…

…nseCallback function.

WebViewJavascriptBridge/WebViewJavascriptBridge_JS.m

@@ -41,6 +41,10 @@ function registerHandler(handlerName, handler) {
 	}
 
 	function callHandler(handlerName, data, responseCallback) {
+		if (arguments.length == 2 && typeof data == 'function') {
+			responseCallback = data;
+			data = null;
+		}
 		_doSend({ handlerName:handlerName, data:data }, responseCallback);
 	}