Fog Improvements (Patreon)

I'm finally starting to figure out how to tweak the fog properly. The falloff of the fog was being compressed by the color shading map algorithm (see the picture from before).

I'm having to make some changes to the algorithm of the color shading map generator to create the color tables for the fog, and since those changes will most likely be not compatible with the color shading tables used for the scrolling sky horizon fading, the fog and the scrolling skies will not be able to share the same color tables.

The "fog" console command was implemented, but still need some improvements. Most notably, fog density can't be properly customized yet. The file format of the fog color tables will also have to be modified to accomodate for the extra parameters involved in their creation.

While taking care of those things I'll also implement the code to activate fog from the map's worldspawn entity.