Add __toString() methods for Description and Tag

And let the Serializer make use of the (string) $tag

src/phpDocumentor/Reflection/DocBlock/Description.php

@@ -209,14 +209,12 @@ class Description implements \Reflector
     }
 
     /**
-     * Returns the exported information (we should use the export static method
-     * BUT this throws an exception at this point).
+     * Returns the long description as a string.
      *
      * @return string
-     * @codeCoverageIgnore Not yet implemented
      */
     public function __toString()
     {
-        return 'Not yet implemented';
+        return $this->getContents();
     }
 }