Put the Serializer version of the Sanitizer through its paces.
Synced with latest HTML5lib. Added preliminary support (currently disabled) for sanitizing REXML trees.
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.
Replaced native Sanitizer with HTML5lib version. Synced with latest Maruku.
