Support multiple references to the same footnote

[yorickhenning]

# Heading

Some text with a footnote.[^1]

Some other text with the same footnote.[^1]

[^1]: The footnote

When rendered, the second paragraph renders the string literal "[^1]" instead of generating a second supertext link to the same footnote.

[ghost]

FYI this plugin does the job: https://github.com/markdown-it/markdown-it-footnote

[Nikaoto]

How exactly would the return link work in this case? Should it add another backlink or just link to the first one? I've circled the backlink, which refers back to the footnote reference 2.