code: function walkPages(pages, drizzleData) {
    if (typeof pages.contents !== 'undefined') {
      return renderPage(pages, drizzleData);
    }
    for (var pageKey in pages) {
      walkPages(pages[pageKey], drizzleData);
    }
    return drizzleData.pages;
  }
docs: Traverse pages data object. render individual pages. An object is
  considered a "page" if it has a `contents` property (otherwise it
  is treated as a (sub-)directory).
  
  @param {Object} pages       pages objects at current level of traverse
  @param {Object} drizzleData all data
  @return {Object} drizzleData, mutated to include updated contents from render