code: function(servers, options) {
      EventEmitter.call(this);
  
      this.servers = servers;
      this.options = options;
      this.prefix = (options && options.prefix) ? options.prefix : "";
  
      if(options) {
          delete options.prefix;
      }
  
      this.memcached = new _Memcached(this.servers, this.options);
  
      var self = this;
      this.memcached.on("failure", function(details) {
          self.emit("failure", details);
      });
      this.memcached.on("reconnecting", function(details) {
          self.emit("reconnecting", details);
      });
  
      if(options && options.customizeKey) {
          this._getKey = options.customizeKey.bind(this);
      }
  }
docs: Toshihiko Memcached
  @param {Object} servers refer to https://github.com/3rd-Eden/node-memcached#server-locations
  @param {Object} options refer to https://github.com/3rd-Eden/node-memcached#options, and you may give a prefix
  @constructor