Allow descriptive text under sections

[lepisma]

At present (probably) adding a new book under a heading just does a single line skip and thus will cause issue when there is description for a section header.

[goderich]

Hi @lepisma ! I've forked your repo and I've been playing around with it, going through your code. I learned a lot, so thank you!
In doing that, I believe I found a few ways to simplify some of your code. Specifically related to this issue, check out this commit.
NB. I prefer to add books to the bottom of their heading, not the top. I'm also unsure if I structure my files different from yours. But I tested it in various situations and it seems to do the trick.

[lepisma]

thanks. would you mind doing a PR here?

[goderich]

I'd like to, but I've made too many changes to my fork! I don't think I can issue PRs anymore, because the history has diverged by now :(

You may not want the rest of the changes I made. Some are strictly for my own convenience.