Execution example::

  select Entries --output_columns 'highlight(body, "Groonga", "<span class=\\"keyword1\\">", "</span>", "mysql", "<span class=\\"keyword2\\">", "</span>", {"normalizers": "NormalizerAuto", "html_mode": true})' --command_version 2
  # [
  #   [
  #     0,
  #     1337566253.89858,
  #     0.000355720520019531
  #   ],
  #   [
  #     [
  #       [
  #         1
  #       ],
  #       [
  #         [
  #           "highlight",
  #           null
  #         ]
  #       ],
  #       [
  #         "Mroonga is a <span class=\"keyword2\">ＭｙＳＱＬ</span> storage engine based on <span class=\"keyword1\">Groonga</span>. &lt;b&gt;Rroonga&lt;/b&gt; is a Ruby binding of <span class=\"keyword1\">Groonga</span>."
  #       ]
  #     ]
  #   ]
  # ]
