Make checker installable as pypi-package

[atmodatcode]

To facilitate installation, it would be worth considering converting the checker into a pypi package

[jkretz]

While not being a full pypi-package yet, a first step into that direction is done in #96

[jkretz]

With #101, we are almost there

[jkretz]

The only thing left for a full pypi packages is to have cc-yaml and compliance-checklib as a pypi package. It will nevertheless be possible to install the checker with a single pip install command referencing this repo. Once this is thoroughly tested, I will add the installation description for it.