Versioning on the Cookiecutter template

[Zeitsperre]

This project was originally on the cookiecutter (using cruft), but we abandoned it due to complications related to the building of Raven-Hydro using newer setuptools versions.

Raven-hydro has since moved to its own Python-based wrapper, so there is nothing preventing this project from adopting a new build engine (flit) and tooling in order to simplify much of the maintenance work.

I propose we do this once Raven-hydro v0.3.1 is released on conda-forge.