The fragment TreeBuilder gains the HTML5 active-formatting-list and reconstruct
step that the document builder already had: when a formatting element (b, i,
em, ...) is closed out of order, it is remembered and re-opened for the
following content. So HTML.parse now agrees with HTML.parseDocument and the
spec, e.g. <b><i></b>X</i> -> <b><i></i></b><i>X</i> and
<p>1<b>2<i>3</b>4</i>5</p> -> <p>1<b>2<i>3</i></b><i>4</i>5</p>. The conformance
corpus that surfaced this now checks the fragment path directly.
Closes#109
Add the PureXML.HTML namespace: a lenient tokenizer for tag-soup input
(case-insensitive tags; quoted, unquoted, and boolean attributes; comments;
doctype; character references), a tree builder handling void elements,
optional end tags (li, p, table rows and cells), raw-text elements (script,
style), and unmatched end tags, and a serializer that writes void elements
unclosed and raw-text content unescaped.
Closes#36Closes#37Closes#38Closes#39Closes#20
