code: function createDirectory(filenames, next) {
          fs.exists(config.folder, function(exists) {
            if (!exists) {
              fs.mkdir(config.folder, function(err) {
                if (err) {
                  next(err);
                } else {
                  next(null, filenames);
                }
              });
            } else {
              next(null, filenames);
            }
          });
        }
docs: Create output directory