This also goes for pkg-config installed by our CMake installation.
This includes
* Updating CMake version on Travis
* Adding a `Catch2` subfolder to the `single_include/` folder to
provide this include path both _inside_ the repository, and _outside_.
* Updated examples to build with the new paths
* Other general CMake cleanup
* Every Linux build tracks coverage when running Debug mode
* OS X not supported yet (Future WIP)
* Our own unit tests, non-default reporters and Clara are ignored