Release checklist

1. All issues closed
2. whatsnew updated
3. debian, conda, ... build and run successfully
4. Tag build
5. conda-forge builds tested (esp. wrt. MUMPS support)
6. Prepare Debian package
7. Upload to PyPI
8. Upload Debian package to launchpad & downloads website
9. Verify that Gohlke's build succeeds
10. Verify that doc links on website point to correct docs (update latest symlink on the docs website
11. Announce release on mailing list & website (blog section)