New world mode: Seasons

A world option like flatworld, or a difficulty setting. The Minecraft world goes through seasons, places that are usually snowy keep their snow year-long and other biomes have snow for x amount of days. In fall, leaves will die and turn shades of red and orange, then eventually turn to snowy leaves (white version of the original texture). Spring will make flowers spawn more frequently and the tick speed for all plants growth would speed up by x amount. Not sure what could be done with summer