[FEATURE] PNG added to the url format

The old URL format http://server/plantuml/img/... is now relaced by
http://server/plantuml/png/...

src/main/webapp/WEB-INF/web.xml

@@ -52,6 +52,10 @@
 		<servlet-name>plantumlservlet</servlet-name>
 		<url-pattern>/form</url-pattern>
 	</servlet-mapping>
+    <servlet-mapping>
+        <servlet-name>imgservlet</servlet-name>
+        <url-pattern>/png/*</url-pattern>
+    </servlet-mapping>
 	<servlet-mapping>
 		<servlet-name>imgservlet</servlet-name>
 		<url-pattern>/img/*</url-pattern>