Point coordinates are in x, y order (easting, northing for projected
coordinates, longitude, latitude for geographic coordinates).
The last point coordinate is implicitly connected with the first.
See also:
Builder::geoWithinPolygon()
See also:
Expr::withinPolygon()
See also:
http://docs.mongodb.org/manual/reference/operator/polygon/
Deprecation:
1.1 MongoDB 2.4 deprecated $within in favor of $geoWithin