Hyperlink DOIs against preferred resolver

Hello :-)

The DOI foundation recommends this new, secure resolver and Zenodo started using it for its badges as well. Accordingly, this PR updates all DOI links.

Cheers!

Thanks. I just spotted this, having been a bit distracted lately. I note that many of the edits relate to a published paper that I'm not sure I should now change, but the Zenodo link I should update. I'll address this later when I can give it proper attention.

Sure, no worries. Since the old DOI URLs are being redirected to the new resolver, there is no need to actually change anything.