Example — 3D scene + post-processing

The same 3D scene as example-3d, run through a postfx graph: a feedback trail
(glowing motion trails) followed by a grade node (chromatic aberration +
vignette). A demonstration of the post-processing API.

Run:  ./VersoDemo --input data/example-3d-postfx.json

CODE:  VersoDemo examples
MUSIC: test.mp3 (placeholder)

If you're using Windows and missing DLLs then install the x64 version of
Microsoft Visual C++ Redistributable for Visual Studio 2019.
