Adds:
- barebones CMakeLists.txt with googletest and doxygen included
- GPL v3.0 or later license
- simple .gitignore
- .clang-format and .clang-tidy
The clang-tidy is only applied within the sources of this project. If it
was included on the top-level CMakeLists.txt it would throw errors on
the gtest compilation.
Let's have some fun!