Multiple corresponding authors

[mpacer]

Right now it seems that if we have more than one author listed as "corresponding author" then it includes a new entry in the footnote for each of those authors. As @eseiver noted on #374 corresponding authors can be multiple authors, however we should not allow non-person authors to list themselves as corresponding authors.

[deniederhut]

👍

[AntoineDujardin]

Right now, it seems that only one author is included.
Furthermore, the note is attached to the first author, whatever the actual corresponding author.
Can I have a non-first corresponding author?