Adjust to an evolutions of html5lib
Adjust to removal of XHTMLSerializer from html5lib and fix and workaround for https://code.google.com/p/html5lib/issues/detail?id=210 https://code.google.com/p/html5lib/issues/detail?id=210

The sanitizer filter seems to be buggy (see also https://github.com/html5lib/html5lib-python/issues/72) so we rely on the sanitizing tokenizer instead
Try a fix for "AttributeError: object has no attribute 'summary_detail'"