Added LeafDecay craftscript

A craftscript that checks every leaf block to see if it wouldn't decay and deletes them if they would.
If you add 
```lua
local E_BLOCK_LEAVES = E_BLOCK_LEAVES
local E_BLOCK_NEW_LEAVES = E_BLOCK_NEW_LEAVES
local E_BLOCK_SPONGE = E_BLOCK_SPONGE
```
in front of this function, does it get faster?