Use common library folder structure

[head5man]

repository root:

cmake/	CMake utilities and package configuration file
examples/	Library examples
include/libname/	Public headers (*.h, *.hpp)
src/	Source files (*.h, *.hpp, *.cxx, *.cpp)
tests/	Unit tests
CMakeLists.txt	Library main CMakeLists.txt
CMakePresets.json	Common configure/build/test presets (CMake 3.19 and newer)