Add support for Google Docs footnotes

[logicalphase]

It's a great add-on and I personally love being able to decouple from the editor and write from a more natural one, but It appears that footnotes are not currently supported. That would be a wonderful feature for those of us who use footnotes.

[georgeh]

Thanks for using the add-on! I'll investigate adding support for footnotes. While I do, is there a Google Doc or blog post using footnotes that you could share with me, so I can see how you are using them?