code: function UDPTracker (client, announceUrl, opts) {
    var self = this
    Tracker.call(self, client, announceUrl)
    debug('new udp tracker %s', announceUrl)
  
    self.cleanupFns = []
    self.maybeDestroyCleanup = null
  }
docs: UDP torrent tracker client (for an individual tracker)
  
  @param {Client} client       parent bittorrent tracker client
  @param {string} announceUrl  announce url of tracker
  @param {Object} opts         options object