Add book and part pages to Latex
If there are explicit parts and/or books, they should be included in the output. Remember, if the title is None, it means it is implicit. If there is an empty title, it means it was explicit, but without a title. Implicit parts and books should not show up in the output, but should explicit ones without titles should just be numbered.
For Latex, the start of each part and book should get its own title page. May need to change things so that chapters are actually Latex sections, because I think there's only one layer above Chapter in latex.