allow items to be numeric

[markhwhiteii]

see the error found in #41 when trying to run eloscoring() on data where the items have numeric IDs instead of character names. a few thoughts:

• this should be limited to just eloscoring—but double-check elsewhere
• I think a simple way to do this would be just to coerce the column to character before running?
• need to implement a unit test for items coming in of different classes