Add module names for the typedoc, make it work

Mark members with @private for typedoc.

tns-core-modules/ui/placeholder/placeholder.d.ts

@@ -1,6 +1,9 @@
 /**
+ * @module "ui/placeholder"
+ * 
  * Contains the Placeholder class, which is used to add a native view to the visual tree.
- */
+ */ /** */
+
 import { View, EventData } from "../core/view";
 
 /**