Release is done through `zest.releaser` and a GitHub CI job:

1. Make sure that your `master` branch is up-to-date:

     $ git checkout master
     $ git reset origin/master --hard
     $ make clean

2. Run `zest.releaser`:

     $ fullrelease

   It will update the version number, push a Git tag and update the
   version number again for the next release.

3. Wait for the GitHub CI job to (automatically) run and publish the
   release on PyPI.
