Integrating clang-format

[novakboskov]

Clang-format is a cross-editor auto-indentation plug-in

The idea is to declare the indentation rules in .clang-format file and
then to use standard editor mechanisms to indent the code using the
exact same indentation rules in all the editors.

Clang-format is already supported in some editors:

• CLion https://www.jetbrains.com/help/clion/clangformat-as-alternative-formatter.html
• VSCode https://code.visualstudio.com/docs/cpp/cpp-ide
• Emacs/Vim via ccls (https://github.com/MaskRay/ccls)