Add dedupe methods to ruby_postal

[jesseclark]

Hi there. First off, I wanted to thank you for all the work you have done on this library. After just a brief exploration of it, it seems like a very valuable resource.

I have a need for deduping of places based on name and address in a ruby application. I have done some testing by writing my addresses out to Geojson, using lieu to dedupe, and then parsing the results which works fine. My ideal situation, however, would be to add and expose the same methods as dedupe.py in pypostal as well as an is_dupe? method similar to the one in lieu's dedupe.py.

I would be glad to take on some of this effort myself but I have not written C bindings for Ruby before. Would you be willing to help/advise me on how to proceed as I dig into it?

Thanks!