JSONP results

Since Placefinder can return a json format, it would be nice if it could wrap the information in "padding," allowing web aps to geocode cross-domain and then provide end users with the resulting data. Currently the only way to do this is to proxy it through a local server. Adding jsonp support is a fairly simple to implement change (add a callback= parameter to allow users to specify a custom callback, and then wrap the data in that callback name.