Allow Windows-builds via CMake

**Is your feature request related to a problem? Please describe.**
Currently, the project cannot be cross-compiled for Windows. It should be compilable on Linux and Windows alike, with the same resulting game application (functionally, not on binary level).

**Describe the solution you'd like**
Extend the CMake configuration and the documentation to allow cross-compilation for Windows if so desired, and retain the original Linux build capabiities.