code: function write(drizzleData) {
    return Promise.all([
      writePages(drizzleData),
      writeCollections(drizzleData)
    ]).then(
      () => drizzleData,
      error => DrizzleError.error(error, drizzleData.options)
    );
  }
docs: Write pages and collection-pages to filesystem.
  
  @param {Object} drizzleData All drizzle data so far
  @return {Promise} resolving to drizzleData