Jekyll::Hooks.register :documents, :post_render do |doc|
  if doc.output_ext == ".html"
    code_block_counter = 1
    doc.output = doc.output.gsub(/(<\/code><\/pre><\/div><\/div>)/) do |match|
      res = match +
              '<div class="plaintext-link"><a href="' +
              "#{doc.url}.#{code_block_counter}.txt" +
              '">plaintext</a></div>'
      code_block_counter += 1
      res
    end
  end
end