Added more item data for vanilla item stacks.

I have exposed a few more properties for item stacks. The compound tag of the item stack is the most interesting as it allows access to data that would otherwise be unavailable. It can also be used to further compare stacks in Lua. I have also exposed the item's max damage to allow for displaying durability as a percentage, as well as checking if the item is even damageable at all. I have also included "maxStackSize" and "isStackable" for good measure. I know I would use all of these quite regularly, I feel as though others would find all of this extremely useful as well.