add clang format
HEy Simon, this MR adds clang-format capabilities to the repo.
It adds a target check-clang-format
for Ci porposes and a target fix-clang-format
for executing before commiting.
In the root folder is the .clang-format which has several options, which we can play around with.
Form the CMake style I'm quite convinced that this is not the way you want to have it but I could imagine a better way.
All the options are given here: https://releases.llvm.org/11.0.1/tools/clang/docs/ClangFormatStyleOptions.html
Edited by Alexander Müller