Add support for returning Confidence level if available.

[niemyjski]

We really need away to capture the relevancy of returned GeocodeAsync calls. For example if I do GeocodeAsync("1002 Main Street") I'm going to get a list of addresses from all over the world. I have no idea which one is more relevant (I get this is somewhat of a bad example, but I know that google returns a confidence score on returned addresses (and field parts like zip code). This would also allow us to sort the results by highest confidence.