Until now, the Zenodo DOI was for the first submission. But now that the
second version is ready to be published on arXiv, I have reserved a Zenodo
DOI.

With this commit, that DOI has been added to the metadata and included in
the paper. Following the publication checklist of 'README-hacking.md', I
also done a spell-check and fixed some minor issues. I also noticed that
'metadata.conf' pointed to the Maneage Git repository, not this project's!