Tone mapping module

Some example projects already implement a pass for tone mapping but it would be much easier to pick from existing functions instead of implementing them manually all the time. Fortunately there's a project on Github providing something like this, even published under MIT license:

• https://github.com/dmnsgn/glsl-tone-map

So this just needs to be implemented as separate module or integrated with the upscaling module as originally planned. However I think it would be pretty neat to have separate for compatibility.