[WIP][CR] Atmospheric and Environmental Modifications to Cities

Applies special zone post processing to generated maps, allowing for things like looted, overgrown, and fungus covered cities.

How it works:
Cities have a zone type added to them, and overmaps have a method to determine if a location lies within a city.  During mapgen, the location checks its city, finds the city zone type, and applies special post processing to it.

Screenshots:
Overgrown with Triffids: http://i.imgur.com/sAEm6lv.png
Overgrown with Fungus: http://i.imgur.com/vr6DQ6x.png
Looted library: http://i.imgur.com/i9VwHY8.png
Looted gun store: http://i.imgur.com/ar2GZbJ.png

Zones so far:
Fungal: the fungus has spread inside and outside of all locations in the area.
Overgrown: triffids have spread nature back into the city, outside areas now full of trees, shrubs, and underbrush.  Some of the road has been broken through.  Inside areas are mostly unaffected, since the plants want the sunlight.
Looted: one in 5 chance of a location being looted, with all items > a certain value (right now $200) and a random amount of the rest being looted, terrain and furniture being bashed up, and blood stains being tossed around.
This sounds awesome. I'm really looking forward to seeing irradiated zones that require PPG to safely cross.