Nonrefactor bugfixes

This PR eliminates #content>#heading, and cleans up/adds several pieces of skeleton/slots related to headings/titles.
Precisely to separate it from the sections in the chapter, and to follow existing convention. Logically a module is a part of a book, and follows the title conventions of chapters -- it is a "section" technically (eg, has a class of .section  as well as .module), but should be treated the same as #part>#chapter. 

This gives us a place to control page breaks, padding/margins, as well as splits the title into its logical parts (.number(), .text(), .divider(), etc -- the same as #chapter.).

We are also able to remove a useless level of (...; section;) from contexts. Eg .style(any; any)/.style(any; any; section) for sections/subsections instead of the .style(any; any; section)/.style(any; any; section; section) we were using before.