Drop DocParagraph from front of headers

I can not remember why they were wrapped in paragraphs to begin with and
it seems unnecessary now that I test it. Closes #307.
Don't mangle append order for nested lists.

The benefit of this is that the ‘top-level’ element of such lists is
properly wrapped in <p> tags so any CSS working with these will be
applied properly. It also just makes more sense.

Pointed out at jgm/pandoc#1346.
Bump haddock-library to 1.1.0 for release