Draft: Update documentation
We need to
- update the Coding Guidelines
- get gitlab-ci working
- for gitlab-ci, but also as preparation for the big migration of the main code, we have to add the external gitlab modules that we will need for the final product:
- modules/PROPOSAL,
- modules/CONEX,
- modules/corsika-data,
- externals/spdlog.
Edited by Ralf Ulrich