Use towncrier for changelog generation

[pedro-psb]

It would be helpful for users to have a changelog file in the repo, especially now that it will show up in the new docs site.

Even though this is not a python package, I don't see a problem in using towncrier for this. Also, it would be nice to use the existing towncrier/commit CI checks to enforce its usage.

[ekohl]

It would be an alternative approach to #46. That approach certainly doesn't provide a changelog in the repo itself.