Gets an ItemStack for the item in the given slot
For the player, slots are indexed with 1 as the main hand, 2 as the off hand, and 3,4,5,6 as the 4 armor slots from the boots to the helmet
If an invalid slot number is given, this will return nil
  overload 1:
                        
user:getItem(index)  
  | Method Property | Fluent Description | Representation | 
|---|
 | index accepts | an Integer |  | 
| Return Value | either an ItemStack or nil |  |