When you build a building or upgrade it, have the ability to add more citizens to the process and decrease time to build or upgrade. 1-4 extra citizens only. Decrease time by 10% per extra citizen. Clearing forests and hunting can use this function as well. Also. Have another library for faster technology upgrades but penalty is 25% more resources is used for 2 researching. 2 blacksmiths, upgrades cost 25% more.