text: Title: Keep orderedness information of lists
  Body: I was wondering if it is possible to know whether a `<list>` in the extracted output came from an `<ul>` or an `<ol>`. Even with `include_formatting` (which I don't need), this information is omitted.
  
  I saw that `<head>`, for instance, retains the level in the `rend` attribute. A similar attribute would be handy in `<list>` as well.
  
  On a related note, description lists (`<dl>`s) are handled even worse, as both `<dt>`s and `<dd>`s are extracted as separate `<item>`s. Something like this:
  - _dt1_: _dd1_
  - _dt2_: _dd2_
  
  would probably serve the purpose better.