Added a podcast.php script that fetches the last X number of sermons from the database and generates an Apple podcast xml feed. It does not interact with the concrete5 code other than read the database connection information.

Added podcast_lib.php which contains a PHP library class to obtain metadata for an MP3 file (from here: http://www.zedwood.com/article/php-calculate-duration-of-mp3). The podcast.php script uses this class to determine the duration of each sermon episode.