code: function (fragmentKey, cachePath, skipCache, callback) {
      if (skipCache) {
        debug('  cache is disabled so...');
        callback(false);
      } else {
        fs.exists(cachePath + '/' + fragmentKey, callback);
      }
    }
docs: Know if content is already in file system
  @param fragmentKey Remote content key
  @param cachePath Temp FS cache directory
  @param skipCache If false, attempt to retrieve remote content from files
  @param callback Method to call when data is retrieved