SqlList<string>() causes a compiler error.

As it stands, this produces a compiler error, due to `System.String` not having a default parameterless constructor. I'm not sure how to go about fixing this, but I think it should be addressed, as I'd imagine it would be a pretty common scenario to want to return a list of strings from a stored proc, using the same API call that you use to return a list of integers or other value types.