Added ability to define polygons and test for geo-point in polygon

This allows you to define geo-polygons (including donut shapes, etc) and test to see if a point is inside a polygon. We're looking to use this with geoJSON so we can use a geo-point and quickly return "state", "country" etc. Technically it should be easy to add any map polygon, e.g. counties, electoral regions, etc. 

Hopefully useful. Note: for some reason geoJSON is lng-lat ordered, it doesn't affect the lib, but the tests use this notation.