Created rpki.util package and __init__.py module
Created RpkiException class in rpki.__init__.py
Created KitchenItemMetadata in rpki.inv.item.py
Several properties in KitchenItem moved to KitchenItemMetadata class
Inventory class rewritten to use KitchenItemMetadata
Added == and != overloads for UPC class as well as a hash function
Renamed UPC.upc property to UPC.code to avoid confusion