complete (opts) {
    if (!opts) opts = {}
    opts = this._defaultAnnounceOpts(opts)
    opts.event = 'completed'
    debug('send `complete` %o', opts)
    this._announce(opts)
  }
Send a `complete` announce to the trackers.
@param {Object} opts
@param {number=} opts.uploaded
@param {number=} opts.downloaded
@param {number=} opts.numwant
@param {number=} opts.left (if not set, calculated automatically)