Get only one item from inventory, directly

[lucmurer]

Status quo:
At the moment Inventory.get() returns a dictionary of items, even if there is only one item.

Proposed enhancement:
Add a method to receive one item directly with the same parameters as the "get" function:

• without the need to extract it from a directory
• which returns None if no such item is found
• which will throw an exception if more than one item is found.