code: function saveFile(filename, data, overwrite) {
    if (overwrite) {
      return fs.outputFile(filename, data)
        .then(() => filename);
    } else {
      return new Promise((resolve, reject) => {
        fsu.writeFileUnique(
          filename.replace(fileExtRegex, '{_###}$&'),
          data,
          { force: true },
          (err, savedFile) => err === null ? resolve(savedFile) : reject(err)
        );
      });
    }
  }
docs: Saves a file
  
  @param {string} filename Name of file to save
  @param {string} data Data to be saved
  @param {boolean} overwrite Overwrite existing files (default: true)
  
  @return {Promise} Resolves with filename if successfully saved