Added in Geospatial support in a similar fashion to GeoDjango

Supports all types of GeoJSON fields and querying using the $geoWithin, $geoIntersects, and $near operators. Allows the developer to use the handy Django operator syntax: e.g.: 
SomeModel.objects.filter(location__near=Point((0, 0)))

Requires GDAL to be installed and a recent-ish version of MongoDB (> 2.6). I've only added support for the newer 2dsphere-index supported operators.

See the tests.gis module for examples of querying