Build system tools and unit testing

Gentle introduction to the basics of CMake and meson, and unit-testing with gtest and catch2.

1. How to generate an executable from several source files organized in sub-folders: 01_basic
2. How to generate a shared library and link your main against it: 02_shared_libraries
3. How to organize your code such that it is modular: 03_modularity
4. How to perform integration tests: 04_tests
5. How to find and use an external library easy: 05a_external_library
6. How to find and use an external library medium: 05b_external_library
7. How to perform unit tests: 06_unit_tests
8. How to customize the build process: 07_customization
9. How compile a code with mpi (brute force) 08a_mpi
10. How to handle mpi dependency 08b_mpi