Release v0.4.0 checklist

[jorisvandenbossche]

• Remove dev0 from the version in __init__.py __version__

• Make a release commit: git commit -m 'RLS: v0.2.0'

• Push the RLS commit git push upstream master

• Make a GitHub release

  • Call the release the current version, e.g. v0.2.0 and pin it to master
  • This will trigger this github action job. Ensure that it completes in the actions tab
    After a few minutes, confirm that the PyPI version is updated
  • If it's a minor/major versoin bump, add some simple release notes.
    If you wish, use [github-activity to generate a changelog](https://github.com/choldgraf/github-activity, eg github-activity pandas-dev/pydata-sphinx-theme --since v0.2.2 --until v0.3.0).

• Bump the __init__.py __version__ and add dev0 to it. e.g.: v0.2.1dev0.

• Commit and push to master

  ```
  git commit -m "dev version bump"
  git push upstream master
  ```
  

• Celebrate, you're done!

Closes #238

[jorisvandenbossche]

https://github.com/pandas-dev/pydata-sphinx-theme/releases/tag/v0.4.0