use the model mapper

[nathantsoi]

this lets you do something like this in the options attr:

item.id as item.name for item in my_rad_items

[amitava82]

Thanks! We should have a readme now.

[Eksrow]

This change seems to break the name of the value being viewed in the selectbox.
So in @nathantsoi case: item.id as item.name for item in my_rad_items

I should be seeing item.name in the selectbox when I select an item in single mode but nothing appears. it works functionally though, item.id does get set as the model value.