Posteriordb now on PyPI

Hi everyone!

We have now made the first release of a Python library to access posteriordb (thanks to @ahartikainen) . The PosterioDatabaseGithub class has been included and works nicely to access posteriors, data, and models. If you need to access a ton of posteriors, you might need to supply a Github personal access token ( GITHUB_PAT) due to the restrictions of the Github API.