Import worddiff.py from stagestosaturn.git
Handle HTML in worddiff.py
Add checkBrackets to verify balancing of brackets
Merge epubbase

Conflicts:
	sanitize.py
Balance brackets (by guessing)

Some of these fixes are bound to be wrong, and need to be verified
against the original book.

There's a legitimate case of unbalanced brackets spanning a paragraph
and blockquote in ch11-6.html, so except that from the checks.