Create higher-granularity breaks in organizational structure

[AABoyles]

R:A-Z is organized into books, sequences, and chapters, and some chapters don't belong to sequences (or even books in some cases). This is also true of The Codex, though not of HPMOR, which is composed of books and chapters without sequences. It would be nice to replicate these organizational structures, instead of just spilling the content in a linear format identical to the reading order of the official compilations.