Added automatic previous/top/next link generation, it's a little
simplistic but it works adequately, certainly much better than nothing.
Added select_one to html, and made HtHtmlElements truthy, so
element = root.select_one('selector')
if element:
   ...

Can be used and does what you'd expect. The behaviour whereby an Element
is truthy if it has children and falsey if it doesn't is depreciated, and
it leads so readily to bugs that I've decided to make ours truthy always.
Improved the warning/errors code especially with reference to multi sutta
mode.
fixes to finalizer