http://www.charlesmerriam.com/blog/2008/04/fun-with-programming-a-technology-tree/
http://www.civfanatics.com/images/civ2/poster/civ2chart.jpg
http://www.charlesmerriam.com/blog/wp-content/uploads/2008/04/civtech.csv
http://www.charlesmerriam.com/blog/wp-content/uploads/2008/04/techpy.txt