fix issue preventing parsing of nested directives.

port to Python 3.

tidied, better spoiler HTML output code, redo bibtex diacritic code.

make use of the HTML5 details tag in html5 output where available,

should still mostly work if not though.

tying into this, improvements to handling of polyglot HTML-XML
script and style tags (when in xhtml mode) in the customised minidom
markup writing code.

minor fix.

HTML writer/renderer compliance improvements. fix some bugs where writer

flags would not be propagated.  add support for illustrative output in
the abandoned XHTML2 format, with and without XHTML5 extensions.
discontinue the separate enamel writer in favour of writer modes.

evolve writenml and more minidom code into writehtml, and improve HTML

writing accordingly with dedicated writer modes.

Code/module/package organisation improvements.

Cleanup for v7.0.0.

Small bugfix for entities inside inline format spans.