Goal of the changes: reduce difficulty overall a bit, and the AI's mid game power (around Renaissance era) especially
Reduced bonus amenities, especially for the eras before Modern Era (now +1 at Medieval, Industrial and every following era at King, Immortal and Pro).
Reduced scaling food bonus to 1% per difficulty per era after Medieval (was 1-8% per difficulty, every era)
Reduced flat science/culture bonus to 3% per difficulty (was 5%).
"Reduced" scaling science/culture bonus to 1-36% per game era and difficulty (was 2-16%; this doesn't look like a nerf, but until Modern Era the AI will actually have less science/culture than before because most the new bonuses are all in the later eras; they will have higher bonuses in the later eras though to compensate)
Other changes:
Added extra builder chargers for the AI (1 extra at Emperor, Deity and Insane).
Removed starting builders for the AI to compensate for the builder buff in the early game.
Bonus starting warriors back to 1-7 from 1-4 for people who choose the option of bonus starting warriors.
Insane only:
The AI now gets 7 bonus Amenities in all cities for the entire game. (compensation for the above nerfs; I didn't want to nerf Insane)