Vector indexes:

Every leaves block has a param2 matching a relative offset (vector). These param2 are invariant by rotating this vector by 90°, so a param2 can match 4 positions (to allow random rotation for schematics).

LEAFDECAY ALGORITHM: if one of the 4 positions matched by the param2 is a trunk, the leaf is not removed.

	x=0	x=1	x=2	x=3	x=4	x=5	x=6	x=7
z=0	0	1	2	3	4	5	6	7
z=1	1*	8	9	10	11	12	13	14
z=2	2*	15	16	17	18	19	20	21
z=3	3*	22	23	24	25	26	27	28
z=4	4*	29	30	31	32	33	34	35
z=5	5*	36	37	38	39	40	41	42
z=6	6*	43	44	45	46	47	48	49

* because invariant by 90° rotation

+50	y=-1
+100	y=-2
+150	y=-3
+200	y=+1

So, param2=1 matches the 4 directly adjacent nodes (horizontally)
param2=8 matches the 4 diagonally adjacent nodes
param2=50 matches the node below

exception: param2=0 (which would match the node itself) is used to disable leafdecay.

Example, with param2 = 123 on node (45,8,-39):
	123 = 100 + 23
	       |    |
	     y=-2  x=2
	           z=3
	relative vectors: (2,-2,3), and by rotation, (3,-2,-2), (-2,-2,-3), (-3,-2,2)
	positions: (47,6,-36), (48,6,-41), (43,6,-42), (42,6,-37)

	(47,6,-36) is air.
	(48,6,-41) is air.
	(43,6,-42) is a tree.
	So, do not remove the leaf.
