def generate_cover!
      return unless @config.cover
      cover_file = MarkupFile.new @config.cover
      markup = Markup::Renderer.new cover_file
      html = "<div class=\"cover\">\n#{markup.render}\n</div>"
      append_stylesheets(html)
      html = add_head(html)
      @coverfile.write(html)
      @coverfile.close
    end
def generate_cover!
      return unless @config.cover
      cover_file = MarkupFile.new @config.cover
      markup = Markup::Renderer.new cover_file
      html = "<div class=\"cover\">\n#{markup.render}\n</div>"
      append_stylesheets(html)
      html = add_head(html)
      @coverfile.write(html)
      @coverfile.close
    end
Generate cover file if optional cover was given