add a changelog (#232)

* add bare changelog

* add changelog entries from https://github.com/python-adaptive/adaptive/releases

* automate the CHANGELOG generation with github-changelog-generator

docker run -it --rm -v "$(pwd)":/usr/local/src/your-app ferrarimarco/github-changelog-generator -u python-adaptive -p adaptive -t TOKEN_HERE

Co-authored-by: Bas Nijholt <[email protected]>
Co-authored-by: Bas Nijholt <[email protected]>

Author: basnijholt