modified config() methods in Core (Playlist, PlaylistElement, FadeInfo,
and AudioClip) to read ID as hexadecimal string & not decimal number
some config xml files and tests had to be modified accordingly
updated config files with title attribute
created getXmlString() method in AudioClip, Playlist, PlaylistElement
and FadeInfo
replaced old (and bad) toXml() method with getMetadataString() in AudioClip