add footnotes support

[Arlind-dev]

I cant get footnotes to work

Example:

Here is a simple footnote[^1]. With some additional text after it.

[^1]: My reference.

Am I doing something wrong?
Markdown render:

Script used: https://cdn.jsdelivr.net/gh/zerodevx/zero-md@2/dist/zero-md.min.js

[zerodevx]

The marked library that zero-md uses does not support footnotes (for now) because it's non-standard. This issue is tracked here. A workaround is here.

Basically Github needs to update the specs so that library authors can handle the footnotes feature and its related edge cases.

[Arlind-dev]

Thanks for the quick response!