Added in treetype, and different tree building code.

Substack tree code and added in guybrush tree code. Set opts.treetype = 2 to change the tree building algorithm.
Moved position of treetype opts.
Not ready for primetime, but has some fractals.

opts.treetype = 3, is a giant floating hegway's dragon.
Add option to disable occupied check

checkOccupied:false will disable the looping to check for occupied
voxels in tree generation (was seeing it loop infinitely).
Merge remote-tracking branch 'tatarize/master' https://github.com/substack/voxel-forest/pull/2

Conflicts:
	index.js