code: function _fileRead(item, callback, err, data) {
    if (err) return callback(err);
    item.data = data;
    callback(null, item);
  }
docs: Updates the item with content of the file.
  @param {Object} item - Object representing investigated file.
  @param {Function} callback - Callback that expects a possible
  error and the item.
  @param {*} err - Possible error passed by caller.
  @param {Buffer} file - Content of the file.