Modern CMake!

• multi-directory source code organisation, separate for headers etc...
• use CPM to grab dependencies such as Catch, for easier testing on CI
• demonstration of where to put public and private header files
• Usage of psuedo-targets in CMake to propagate project-wide options, rather than setting them globally
• CMake project is exported properly such that it can be found automatically by other CMake projects once installed (install(EXPORT))