New UTI: .mdown

[iRouge]

I don't know if it's a legitimate UTI. I've encountered it a few times (in private repos; sorry, I can't provide a link for now). This is more of an annoyance, but it would expand the excellent coverage of QLMarkdown.

[sbarex]

It isn't clear to me—is .mdown the file extension? If it is a format registered by a specific application, you also need to know the exact uti with this code form the Termina.app:

tmp_file=/tmp/test.mdown; touch "$tmp_file"; mdls -name kMDItemContentType --raw "$tmp_file"; rm "$tmp_file"; tmp_file=