Improve Documentation

[tornede]

Improve Documentation

• Add documentation using Sphinx, therefore a workflow is created to build and push the website
• The build documentation will be pushed to a separate branch gh-pages

Update code documentation of PyExperimenter (#65)

• The API of the class PyExperimenter has been updated and documented

Convert project to pyproject.toml using Poetry (#54)

• Create pyproject.toml via Poetry
• Add all dependencies for PyExperimenter itself as well as for the development
• Update the installation description within documentation of PyExperimenter
• Update How-to-Contribute documentation to cover Poetry
• Update development workflow of How-to-Contribute documentation to cover all necessary steps

Add workflow to automatically check tests (#55)

• Adds a simple test runner using GitHub Actions.
• Uses poetry to install the package and locked dependencies.
• Caching the virtual environment. This prevents having to install it every time and cuts down on CI roundtrip times.
• It tests a matrix of various python versions (3.7, 3.8, 3.9) and OS versions (Ubuntu, MacOS, Windows). Python 3.10 is excluded for now, since installing some of the dependencies takes a very long time.