Completely removed the html5lib sanitizer.
Fixed the string-handling to work in both
Ruby 1.8.x and 1.9.2. There are still,
inexplicably, two functional tests that
fail. But the rest seems to work quite well.
Fixed a bug in the HTML5lib tokenizer (affects S5 slideshows).
Some miscellaneous code cleanup. In particular, don't bother with zapping control characters;
instead, rely on is_utf8? method to raise an exception (which we do anyway).