code: function parseGlossary(book) {
      var logger = book.getLogger();
  
      return parseStructureFile(book, 'glossary')
      .spread(function(file, entries) {
          if (!file) {
              return book;
          }
  
          logger.debug.ln('glossary index file found at', file.getPath());
  
          var glossary = Glossary.createFromEntries(file, entries);
          return book.set('glossary', glossary);
      });
  }
docs: Parse glossary
  
  @param {Book} book
  @return {Promise<Book>}