Better Forests

Major changes:

Trees for Dark Forest. Dark Forest darkness varies, causing the spawning rate to vary from place to place. Put Better Trees into Windswept Forest and Windswept Savanna Attempts to move game start spawn in trees to ground.

Minor design changes Increased average size of Savanna trees. Leafier large birch More branches on medium spruce. Lowered chance of beehives Enabled Better Trees to generate below y=64 Adjustments to savanna trees Less variability in swamp tree density

Debugging

Fixed a deep bug in the tree branch code. Trees generate properly over water.

Internal changes Made variable tree reentrant for multiprocessing Better performance on initial world generation. Moved control of light level from trees to biomes.