Releasing pykdtree

Add release information to README.rst
Update version number in setup.py
run loghub and update the CHANGELOG.md file and commit the changes:
```
loghub storpipfugl/pykdtree --token $LOGHUB_GITHUB_TOKEN  -st $(git tag --sort=-version:refname --list 'v*' | head -n 1) -plg bug "Bugs fixed" -plg enhancement "Features added" -plg documentation "Documentation changes"
```
This uses a LOGHUB_GITHUB_TOKEN environment variable. This must be created on GitHub and it is recommended that you add it to your .bashrc or .bash_profile or equivalent.

This command will create a CHANGELOG.temp file which need to be added to the top of the CHANGLOG.md file. The same content is also printed to terminal, so that can be copy-pasted, too. Remember to update also the version number to the same given in step 5. Don't forget to commit CHANGELOG.md!
Create a git annotated tag by running:
```
git tag -a vX.Y.Z -m "Version X.Y.Z"
```
Push to github with:
```
git push --follow-tags
```
Wait for tests/actions to pass on GitHub.
Click "Draft a new release" at https://github.com/storpipfugl/pykdtree/releases. Title it "Version X.Y.Z" and include the release notes for this version in the description.

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