add extra section for shell-deferring
remove "continues now". It feels awkward
link to py2guile
nagware: say version, not preview, to avoid looking like the book stops here
only nag before one in 3 chapters, selected at random
Nagging before each chapter seriously impedes on the reading experience.
add 'continues now' to nagware to ensure that people don't drop out
Make nag page clickable.
fix abstract in title: must use lowercase begin_abstract.
add nagware for the free preview
regular font for authors is better readable
Add free preview note to the info.
add the link to the book.
add ebook ISBN
only up to 6 levels of headlines (epub does not support more)