code: function(callback) {
        var t = this;
        async.waterfall([
          function readDb(callback) {
            fs.exists(t.__dbFilename, function(exists) {
              if (exists) {
                fs.readFile(t.__dbFilename, {
                  encoding: "utf-8"
                }, callback);
              } else {
                callback(null, null); 
              }
            });
          },
  
          function parseDb(data, callback) {
            t.__db = data && data.trim().length ? jsonlint.parse(data) : {};
            callback(null, t.__db);
          }
        ], callback);
      }
docs: Loads the cached database
  
  @param callback