Removed writerDocbookVersion in WriterOptions.
Renamed default.docbook template to default.docbook4.
Allow docbook4 as an output format.
But alias docbook = docbook4.
The "default" option is no longer represented as `Nothing` but via a new
type constructor, making the `Maybe` wrapper superfluous.
The default behavior of using heuristics can now be enabled explicitly
by setting `--top-level-division=default`.
API change (`Text.Pandoc.Options`): The `Division` type was renamed to
`TopLevelDivision`. The `Section`, `Chapter`, and `Part` constructors
were renamed to `TopLevelSection`, `TopLevelChapter`, and
`TopLevelPart`, respectively. An additional `TopLevelDefault`
constructor was added, which is now also the new default value of the
`writerTopLevelDivision` field in `WriterOptions`.
Pandoc uses heuristics to determine the most resonable top-level
division type when emitting LaTeX or Docbook markup. It is now possible
to overwrite this implicitly set top-level division via the
`top-level-division` command line parameter.
API change (`Text.Pandoc.Options`): the type of the
`writerTopLevelDivision` field in of the `WriterOptions` data type is
altered from `Division` to `Maybe Division`. The field's default value
is changed from `Section` to `Nothing`.
Closes: #3197
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.
