Made the title property optional

Author: Martin Brecht-Precht

src/HandlerInterface/HandlerInterface.php

@@ -192,14 +192,14 @@ public function onLineBreakContent($hard);
 	 * @param string $title
 	 * @return void
 	 */
-	public function onLinkContentBegin($uri, $title);
+	public function onLinkContentBegin($uri, $title = null);
 
 	/**
 	 * @param string $uri
 	 * @param string $title
 	 * @return void
 	 */
-	public function onLinkContentEnd($uri, $title);
+	public function onLinkContentEnd($uri, $title = null);
 
 	/**
 	 * @param string $text