Fixed #14 Filter HTML into XML upon loading document
DOMTemplate is now more lax on what it accepts as HTML, various XML conversions are run to make it ready for PHP DOM:
* HTML entities decoded to unicode
* Elements that require it are self-closed (e.g. `<img>` -> `<img />`)
* HTML valueless attributes are converted to XML, i.e. `<a attr>` -> `<a attr="attr">`
* Script elements are escaped with XML CDATA blocks
These XML-isms are reversed when outputting as HTML