Footnote refs

[flying-sheep]

Need to rework the numbering logic, probably no way to get around having the parser track state …

It should work this way:

1. names/refnames are not used
2. IDs are independent from visible label. Named footnotes have that name as ID, others have footnote-n with an independent running counter in docutils (maybe stick with UUIDs for now). footnote references have footnote-reference-m with a different independent running counter)
3. the visible label counter depends on footnote order only (not references), so the references [#]_, [#]_ can become [1] [3] if the footnotes are .. [#], .. [#named], .. [#]. that means that we probably need one more pass (1. assign order to numbered (and symbol) footnotes, 2. resolve footnote references, 3. add backrefs to footnotes)