Reconsider NominalElementDictionary

[dabrahams]

As I have been working on InsertionOrderedDictionary, I've started to wonder whether NominalElementDictionary was such a hot idea. Instead, maybe the thing to do is make an extension on Dictionary called nominalElements that presents the (key: Key, value: Value) elements as a Collection of KeyValuePair<Key, Value>. When people need the capabilities associated with a collection of KeyValuePair, they can use this extension. Otherwise it just sits there.

Part of the reason for this is that you lose convenient destructuring that was available with tuples. Part is the massive complexity overhead of making the whole dictionary API just in order to be able to use Collection where Element: SomeProtocol extensions.

/cc @saeta @marcrasi

[dabrahams]

Or even project Tuple2's, and drop KeyValuePair.