code: function StatsdClient(opts) {
    BaseClient.apply(this, arguments);
    opts = opts || {};
    this.host = opts.host || '127.0.0.1';
    this.port = opts.port || 8125;
    this.keyBuilder = opts.keyBuilder || defaultMetricsKeyBuilder;
    this.socket = dgram.createSocket('udp4');
  }
docs: A client that can send metrics data to a statsd backend
  @param {Object} opts options about the statsd backend
  @param {String} opts.host the host of the statsd server. Default is 127.0.0.1.
  @param {Number} opts.port the port of the statsd server. Default is 8125.
  @param {Function} opts.keyBuilder a function that will be used to format the meta data of a metric into a single key value. The signature of function is like this: function(key, tags, fieldName)