* @param string filename optional the filename where a recent version of the feed is saved. If not specified, the filename is $_SERVER["PHP_SELF"] with the extension changed to .xml (see _generateFilename()).
* @param boolean displayContents optional send the content of the file or not. If true, the file will be sent in the body of the response.
* @param filename string optional the filename where a recent version of the feed is saved. If not specified, the filename is $_SERVER["PHP_SELF"] with the extension changed to .xml (see _generateFilename()).
* @param timeout int optional the timeout in seconds before a cached version is refreshed (defaults to 3600 = 1 hour)