Additionally, footnotes are now parsed similar to the corresponding reStructuredText, in that resolution (between definitions and references) and ordering is now deferred to transforms on the doctree (in gh-pr:931).
This allows for the proper interaction with other docutils/sphinx transforms, including those that perform translations,
and logging of warnings for duplicate/unreferenced footnote definitions and also for footnote references with no definitions.
This change makes the slug generation closer to GitHub, in that, starting/ending whitespace will not be stripped.
For example, # ` a` b `c ` will now correctly create the slug -a-b-c- and not a-b-c
