#240 Try out clang-tidy

[Ulf Lorenz]

What and Why

In principle, clang-tidy can do pretty powerful code checks and automatic refactorings, but the full list is so large as to be overwhelming.
Figure out and define the checks and refactorings that may make sense and document them so that they are run regularily (at least manually in the absence of CI).

Todo

• learn about the various clang-tidy checks and refactorings and choose a suitable subset
• apply the clang-tidy checks/refactorings
• document them to run them regularily