More explicit warning about large maps causing memory crashes 

Catch base terrains with occursOn in ruleset validation

Removing improvement-creating buildings where the no city tile has the improvement, no longer crashes

Cities can attack revealed invisible units

By Ambeco:
- Adding alternate pathing algorithm 
- Jungles again no longer spawn on hills 
- MapGeneration ignores rareFeatures when placing normal tiles 

Add max(), min() functions to countable expressions - By AutumnPizazz