created GeoNamesAPI::NearestIntersection for 'nearest intersection' endpoint

Hello,

Added basic support for this additional endpoint. (Not currently supporting the 'filter' parameter: http://www.geonames.org/maps/us-reverse-geocoder.html#findNearestIntersection.)

For my own sake, too, I want to make this robust. Any other tests I should write, or stuff I should build in? Very open to constructive feedback, especially as I'm not too familiar with this codebase.


Thank You,
James Cropcho (@cropcho)