Release fmf-1.6.0

[psss]

Follow the steps below to create a new major or minor release:

• Update README.rst with new contributors since the last release
• Review the release notes in releases.rst, update as needed
• Add a Release x.y.z commit, empty if needed: git commit --allow-empty -m "Release x.y.z"
• Create a pull request with the commit, ensure tests pass, merge it

Create a new github release based on the tag above

• Move the fedora branch to point to the new release
• Tag the commit with x.y.z, push tags git push --tags
• Create a new github release based on the tag above
• Mention the most important changes in the name, do not include version
• Push the “Generate release notes” button to create the content
• Publish the release, check Fedora pull requests, make sure tests pass and merge
• Close the corresponding release milestone