After further testing, it seems promotions given by forts still cause random crashes. I have disabled that piece of code, until I figure it out why.

v4 Changes:

1) Fixed bugs related promotions given by forts and citadels.
2) The radius of uncovered plots around cities depends on the defensive buildings built by that city.
3) Defensive wonders (Great Wall, and Great Firewall), completely envelop the country in fog (in respect of other players)
4) Tweaked the probability algorithm so that, as you discover more area, there is more varied "fogging". To put it simply fog grow will be more varied.
5) Added a few more settings, in the script.

v3 Changes:

1) Minor fix, where forts and citadels would give promotions to dead units and crash the game.

v2 Changelog:

1) This mod no longer requires Community Patch to run, but some features might require it to work properly.
2) The fog now has a probability to grow. This probability decreases as you research exploration techs like Optics, Compass, Astronomy, etc.
3) Forts, that you built, will stop fog from growing. This feature requires Community Patch.
4) There is now a fully flushed out settings panel within the FogScript, where you can tweak almost anything within this mod. From what types of plot to fog, probability of fog (related to techs), number of plots to fog, etc. I highly recommend navigating to Core/LUA/GFOW_FogScript.lua, and tweaking these settings. There are a lot of them.
5) Removed "Reveal Map" goody , for obvious reasons.
6) Forts and citadels provide units extra sight. Special thanks to @zArkham4269 for suggesting this.
7) Fixed bug, where resource icon remains, even if the fog rolls over it. There is still a setting within the script that allows you to re-enable this.