MapQuest Support + Batch Request

Hi,

I'm not sure if this would be helpful to you or anyone else but I needed MapQuest & Open Street Map support for one of my project & found Geocoding.net to be an excellent starting point so I extended your library and added MapQuest support & batch support (MapQuest / OSM only for now).

I also added some XUnit tests and it is working great for me.  Let me know if you have any question.

--Huy