#299: Geopoint field type

As discussed in issue #299 I added functionality to define in schema geojson types. Validations added.
http://geojson.org/geojson-spec.html

TBH I was thinking of adding indexing as well, using geohashing, but I prefer to pull by parts.
According to the [specification](http://geojson.org/geojson-spec.html#geojson-objects)

> The GeoJSON object may have any number of members (name/value pairs).