Add support for tutorial links to makerst.py

Also change the <tutorials> structure to make use of individual <link> tags

modules/visual_script/doc_classes/VisualScript.xml

@@ -9,7 +9,7 @@
 		You are most likely to use this class via the Visual Script editor or when writing plugins for it.
 	</description>
 	<tutorials>
-		http://docs.godotengine.org/en/3.0/getting_started/scripting/visual_script/index.html
+		<link>http://docs.godotengine.org/en/3.0/getting_started/scripting/visual_script/index.html</link>
 	</tutorials>
 	<demos>
 	</demos>