Revised caseTransform to use a fold.

This shouldn't change anything, but it allows us in the future
to pay attention to sequences of characters, not just individual
characters.
Improved case transform.

Previously capitalization might change after a word-internal period.

Now internal punctuation only signals a word boundary if it is
a dash or single quote character.

See
https://groups.google.com/d/msgid/pandoc-discuss/5370FE00.1050808%40reagle.org

Thanks to Joseph Reagle for reporting.