Item prototypes use unique codes to keep them differentiated.  This is important for savefiles
since items may change between game versions.  The savefile stores the unique code and attempts to
restore the item to the inventory from the code.

If a code is deprecated, mark it as such.

Numbers below 1 are invalid.  0 is invalid as it's a system code, negatives are invalid as the file
saves unsigned integers.

Code - Item
   1 - Sweet Apple

 200 - Applejack's Hat