function parseString (xml, callback) {
  var doc, error, plist;
  try {
    doc = new DOMParser().parseFromString(xml);
    plist = parsePlistXML(doc.documentElement);
  } catch(e) {
    error = e;
  }
  callback(error, plist);
}
Parses a Plist XML string. Returns an Object. Takes a `callback` function.

@param {String} xml - the XML String to decode
@param {Function} callback - callback function
@returns {Mixed} the decoded value from the Plist XML
@api public
@deprecated not actually async. use parse() instead