This fixes a small mistake where the "raw" status wasn't being reset
once exiting the script or style tags. That means any text nodes that
followed would be misinterpreted as being raw.
This adds a bunch of tests to better exercise the HTML rendering and to
be able to track any changes in its behavior.
This includes a new `check_all_main_files` to more conveniently check
the HTML content of every chapter in a book.