Add MSMD dataset

[stefan-balke]

No description provided.

[lostanlen]

Hi @stefan-balke, are you sure that you want to give a link to the GitHub CPJKU/msmd?
Why not directly the Zenodo page? https://zenodo.org/record/2597505/
The former may go 404 one day; the latter won't.

[stefan-balke]

Yes, either or is fine. IMHO, you need both for this dataset.

[lostanlen]

Then it would be good to bundle the v1.1 code on Zenodo alongside the ZIP file?

[ejhumphrey]

to be fair, they both may 404 someday, because the internet is an ephemeral web of transience.

but! this raises an interesting limitation of the schema – what if there are mirrors? or multiple related sites? should url be an array? or do we need a separate mirrors or additional_urls field? I've added #17 for that discussion. I'm fine with leaving these changes as-is, and revisiting what to do with multiple URLs going forward.

[ejhumphrey]

doing a little cleaning on this, @lostanlen or @stefan-balke do you have any updated opinions on this?