Feature Request: Add Support for Footnotes

[fusion809]

Hi,

I would like footnotes of the form: [^X] (where X is a positive integer, e.g., 1,2,3,...) to be supported by this package. Here is an example in-text footnote of this form (that you can use for testing out any changes you make to this package):

operating systems are not 100% free and open-source,[^1]

and at the end of the document here is the full footnote definition:

[^1]: Systems that are entirely free and open-source I will refer to as *libre* to distinguish them from those that are not.

Thanks for your time,
Brenton

[dcd-arnold]

It is an offical part of GFM now: https://github.blog/changelog/2021-09-30-footnotes-now-supported-in-markdown-fields/