Feature Request: Contrast post-processing effect

Similar to:

```pre
				cameraEffectShader = RPM/Greenscale
				cameraEffectVariables = _Gain,2.5
```
in order to 'fake it' when trying to do night vision... it would help (be awesome) to have a contrast ability :)

```pre
				cameraEffectShader = RPM/Greenscale
				cameraEffectVariables = _Gain,2.5|_Contrast,float
```


Cheers!