Let `GetMultipleItems` accept a list of ID strings

[eike-welk]

Currently shopping.GetMultipleItems expects the item IDs as a single string with comma separated values. This is inelegant, because a Python program normally stores item IDs in a list of strings, or generally in an iterable. Writing before the call to GetMultipleItems:

ids_str = ",".join(ids)

Is not a big pain, but this line should be IMHO in GetMultipleItems. Therefore:

Please modify shopping.GetMultipleItems, so that its argument item_id accepts an iterable that contains item ID strings.