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.
Previously, used a regexp to find and convert named entities in the content.
Now use a more efficient algorithm.
Similar tweak for converting NCRs before checking whether text is valid utf-8.
