code: function walkPages(pages, drizzleData, writePromises = []) {
    if (isPage(pages)) {
      return writePage(
        pages.id,
        pages,
        drizzleData.options.dest.pages,
        drizzleData.options.keys.pages.plural
      );
    }
    for (var pageKey in pages) {
      writePromises = writePromises.concat(
        walkPages(pages[pageKey], drizzleData, writePromises)
      );
    }
    return writePromises;
  }
docs: Traverse pages object and write out any page objects to files. An object
  is considered a page if it has a `contents` property.
  
  @param {Object} pages   current level of pages tree
  @param {Object} drizzleData
  @param {Array} writePromises All write promises so far
  @return {Array} of Promises