One thing I noticed was that there is still improve.txt, but it doesn't seem to be used; instead I think buildings.txt is used. I haven't changed anything in it yet, but it seems some of the buildings in the game aren't in improve.txt but they are in buildings.txt. Also there are no numbers at the top of the file, (wonders.txt either), I wonder if the numbers are stored somewhere else or if they got rid of them altogether.

In wonders.txt they changed how wonders give buildings to all cities. Instead of strings for specific buildings they now have a general one that you combine with the string for the building you want:

BuildingEverywhere IMPROVE_CITY_WALLS

I've tried it and it works great. I hope this helped somebody, I'd hate to think I wasted my time.