html2book 6.x-1.0

Official release of D6 version.

Lots of work done on a D6 port by junedkazi, progesterone, and levavie, so thanks so much to them (see http://drupal.org/node/253587).

- Added a new feature to allow you to mark what headings you want to use to split pages on. So you might only want new pages at <h1>, <h2>, and <h3>, but not at lower levels.
- Miscellaneous code cleanup and Help cleanup.