Markdown footnotes -- prepend generated id

[digitalresistor]

Enhancement

Environment

Zola version: 0.12.2

Prepend footnote id's with fn: or other unique tag.

I have an id collision that is happening on my main page after rendering because an article has an header that matches the name of a footnote. This means that when displaying multiple full articles on the same page, the id matches and it links to the wrong location.

I have started manually prepending the date to the footnotes so that hopefully it is enough to disambiguate them.

[Keats]

We currently use the basic pulldown-cmark footnotes with no further special handling. If we want to do things like (as well as your #1285) someone would need to take on the lead on implementing it.

[digitalresistor]

Ah, alright.

Looks like there is some other footnote related work going on there too: pulldown-cmark/pulldown-cmark#464