Removes the given ItemStacks from the inventory.
It will try to remove 'as much as possible' from the types and amounts you give as arguments.
The returned HashMap contains what it couldn't remove, where the key is the index of the parameter, and the value is the ItemStack at that index of the varargs parameter. If all the given ItemStacks are removed, it will return an empty HashMap.
@param items The ItemStacks to remove
@return A HashMap containing items that couldn't be removed.
@throws IllegalArgumentException if items is null