Indent.
Prioritize autolink below html.

Pandoc does it the other way around, but, we're not trying to be fancy
about autourl parsing (i.e. is it a valid URL or email).
A quick hack for `img` tags lacking a closing `/`

Need to loop back and deal with this both:

1. More generally -- not just `img`, but the full list of such tags.

2. More correctly -- currently if someone does <img></img> we don't
"eat" the trailing </img>.