Add links as footnotes

[atymic]

Hey!

Our use case for this package is transforming user supplied rich text into plain text for platform that do not support HTML. Keeping links is the goal, but we can't use HTML. Would you accept a PR for creating footnotes with the links?

Something similar to what most mail clients do https://help.icontact.com/customers/s/article/Links-and-Footnotes-in-Plain-Text-Emails

[stevebauman]

Hey @atymic,

Would converting the links into markdown work for your use-case? I.e.:

[Example Link](https://example.com)

[atymic]

Hey @stevebauman Hmm, that could work. i'll have a test with the calendar platforms and see :)