+ Re-use `toTocTree` in constructing `chunkedTOC`.
Previously we used an entirely different function toTOCTree'.
+ Improve `tocToList` so that it avoids empty lists of
items that are omitted because they are below the toc depth.
pandoc-lua-engine:
+ Fix structure tests in light of last change.
T.P.Writers.ChunkedHTML:
+ Reuse `tocToList` in `buildTOC`.
T.P.Writers.EPUB:
+ Adjust EPUB writer for Chunks changes.
Adds support for table of contents and chunks handling. The function
`make_sections` has been given a friendlier interface and was moved to
the new module; the old `pandoc.utils.make_sections` has been
deprecated.
John MacFarlane