This PR introduces the generation of documentation based on
this excellent blog post: https://devblogs.microsoft.com/cppblog/clear-functional-c-documentation-with-sphinx-breathe-doxygen-cmake/
It combines the tools Sphinx, Doxygen and Breathe to generate good
looking HTML documentation conveniently which can be hosted easily.
The helper scripts were unified and there is now one helper.py script
which can be used to create, build and open both tests and documentation.
"./helper.py -h" can be used to get the different options.
This PR also contains some smaller fixes which were necessary for the docs
to build
This PR refactores the tests so they are built as part of the FSFW.
This is done by adding Catch2 with the FetchContent directive.
A future implementation might also use a system installation of Catch2
by first checking whether Catch2 can already be found as a package
The custom configuration folder testcfg was moved from the user folder
to the actual unittest folder.
The tests can be built by setting the CMake FSFW_BUILD_UNITTESTS option
to TRUE/ON. They are built with the static library and dropped inside
the build folders fsfw directory.