Releasing pycldf

Do platform test via tox:
```
tox -r
```
Make sure statement coverage >= 99%
Make sure flake8 passes:
```
flake8 src
```
Make sure the docs render:
```
cd docs
make clean html
cd ..
```
Update the version number, by removing the trailing .dev0 in:
- setup.cfg
- src/pycldf/__init__.py
- docs/conf.py
- and edit CHANGELOG.md
Create the release commit:
```
git commit -a -m "release <VERSION>"
```

Create a release tag:

git tag -a v<VERSION> -m"<VERSION> release"

Release to PyPI:

rm dist/*
python -m build -n
twine upload dist/*

Push to github:
```
git push origin
git push --tags
```
Change version for the next release cycle, i.e. incrementing and adding .dev0
- setup.cfg
- src/pycldf/__init__.py
- docs/conf.py

Commit/push the version change:

git commit -a -m "bump version for development"
git push origin