Fix epub TOC

[kthoden]

TOC has problems with subelements: ´´´1. Alvarus Thomas und sein ´´´ instead of ´´´1. Alvarus Thomas und sein Liber de triplici motu´´´.

The latter was produced using the Book edit tool of Calibre. Maybe the final mastering of the ebook should be done via Calibre, also possible via command line http://manual.calibre-ebook.com/polish.html