Start work (which may not pan out) on a new sanitizer. Right now, it passes
all but 1 of the HTML5lib Sanitizer's unit tests. But it doesn't do much
of anything to ensure well-formedness. This is not an issue for Maruku-processed
content, but it is a concern for <nowiki> blocks.
(One solution would be to use the HTML5lib parser on <nowiki> blocks.)
In any case, this baby is 3 times as fast as the HTML5lib sanitizer.
Synced with latest version of HTML5lib, which fixes problem with Astral plane characters.
I should really do some tests, but the HTML5lib Sanitizer seems to be 2-5 times slower than the old sanitizer.
