renumber footnotes

[yshavit]

If I have a footnote [^a], it gets rendered by GFM as ^[1] — not ^[a].

I should accordingly canonicalize the footnotes on output, so that they look like the text they'll eventually become.

This should be an option, defaulting to on.

[yshavit]

Testing the interaction of footnotes and link references:

[hello][3], world[^3] [^a] [^1] [^shortcut] [^collapsed][].

[3]: https://example.com
[^a]: a footnote
[^3]: this is my footnote text.
[^1]: my second footnote text.
[^shortcut]: my shortcut footnote text.
[^collapsed]: my collapsed footnote text

results in:

hello, world^{1 2 3 4 5}[].

So it looks like:

• links and footnotes are in different namespaces
• shortcut footnotes work
• collapsed footnotes are treated as shortcut (with an additional [] as just plain text)
• GitHub's rendering renumbers all footnotes, starting at 1

Footnotes

1. this is my footnote text. ↩

2. a footnote ↩

3. my second footnote text. ↩

4. my shortcut footnote text. ↩

5. my collapsed footnote text ↩