Release tasks

[petrelharp]

For nex time:

• [x] - make sure you're on main
• [x] - increment the version in pyslim/_version.py
• [x] - update CHANGELOG
• [x] - commit and tag
• [x] - update tags on github with git push; git push --tags
• [x] - upload to pypi:

  python3 setup.py sdist bdist_wheel
  twine upload dist/FILES_TO_UPLOAD

• [x] - check on pypi that the update actually worked
• [x] - check tskit-site build succeeded
• [ ] - upload to zenodo
• [ ] - update version and DOI in CITATION.cff (once added)
• [x] - conda-forge: will do an automatic PR (winni2k says: "The key things I checked were that the version number is correct, the SHA sum has changed, and that the build number is reset to zero. Any other problems should be caught by the automated build system."
• [ ] - email SLiM list

Post-release:

• [ ] update code in tskit-site workflow to get right pyslim/SLiM version
• [x] make copy of this issue for the next release

Reference: https://packaging.python.org/tutorials/packaging-projects/