mo_os: simplify call signature; respect mo_message settings

See merge request !72

finalize v0.4.0

See merge request !71

Add logging

See merge request !63

Add module for sentinel handling

Closes #37

See merge request !64

refactored .gitlab-ci.yml

Closes #39

See merge request !68

mo_message: simplify; add global option to show messages; add raise option

See merge request !69

# Conflicts:
#   README.md
#   src/mo_message.F90

license update

See merge request !66

git subrepo clone --branch=v1.6 --force https://git.ufz.de/chs/HPC-Fortran-module-loads.git hpc-module-loads

subrepo:
  subdir:   "hpc-module-loads"
  merged:   "e9463a0"
upstream:
  origin:   "https://git.ufz.de/chs/HPC-Fortran-module-loads.git"
  branch:   "v1.6"
  commit:   "e9463a0"
git-subrepo:
  version:  "0.4.3"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "2f68596"

git subrepo clone (merge) --branch=v2.0 --force https://git.ufz.de/chs/cmake-fortran-scripts.git cmake

subrepo:
  subdir:   "cmake"
  merged:   "87a4b64"
upstream:
  origin:   "https://git.ufz.de/chs/cmake-fortran-scripts.git"
  branch:   "v2.0"
  commit:   "87a4b64"
git-subrepo:
  version:  "0.4.3"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "2f68596"

git subrepo clone --branch=v2.1.0 --force https://github.com/jothepro/doxygen-awesome-css.git doc/doxygen-awesome-css

subrepo:
  subdir:   "doc/doxygen-awesome-css"
  merged:   "a3c119b"
upstream:
  origin:   "https://github.com/jothepro/doxygen-awesome-css.git"
  branch:   "v2.1.0"
  commit:   "a3c119b"
git-subrepo:
  version:  "0.4.3"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "2f68596"