The `--chapters` option is replaced with `--top-level-division` which allows
users to specify the type as which top-level headers should be output. Possible
values are `section` (the default), `chapter`, or `part`.
The formats LaTeX, ConTeXt, and Docbook allow `part` as top-level division, TEI
only allows to set the `type` attribute on `div` containers. The writers are
altered to respect this option in a sensible way.
These are primarily aimed at testing the new treatment of line breaks,
but hopefully other tests can be added more easily now as features
and changes are implemented in the writer.
Adapted from Tests.Writers.HTML.tests.
