Add a benchmark example project

[domme]

We don't have much visual things to show yet - just some small test-projects that are meant for continous testing of the underlying API. We should add a small benchmark example project to change that. In its first iteration, it could be a simple scene with basic PBR lighting. In the future, it could be used to incorporate more and more features and eventually becomes a dedicated project that can be separated from FANCY and just uses it as a library.