More custom drop options

CRAFTBOOK-3078 - Reported by Nabawi.Azizul

Is it possible to make another drop depend on what you use?

For example :
IronOre:
block: "IRON_ORE"
drops:
CobblestoneExplosion:
item: "COBBLESTONE:0"
chance: 100
require: EXPLODE or CREEPER //environment effect
Rock:
item: "SNOW_BALL:0"
chance: 30
require: HAND //either holding blocks or not
IronOre:
item: "IRON_ORE:0"
chance: 100
require: tool_pickaxe //any pickaxe
IronIngot:
item: "IRON_INGOT:0"
chance: 100
require: "DIAMOND_PICKAXE" //specific item (with meta support?)
type: block
append: false

"require:" is a command which items/blocks they can use in order to get the drop.
It can use any items, blocks and event environment effect.
If it's not using "require:", it can be earned in any way.

Well, if "require:" sounds silly, you can change it. I'm not the smart enough to think one.

Mini request, can you make decimal number for percentage?