Change data structure to fit geofirestore-js

[Lorenzo Calisti]

Change the data structure from this

{
   "g": "",
   "l": "",
   ...
}

To this

{
   "g": "",
   "l": "",
   "d": {
        ....
   }
}

In order to support the users of the geofirestore-js library.

[Lorenzo Calisti]

I think the structure of the library shouldn't change because of backward compatibility and because it's the unique mark of this library.
Currently, I'm working on an update that will use as default a GeoPoint for "l", but still accept a list like the current model, with this update all the data created by geofirestore-js will be readable by the library as expected, the only problem is when creating the data with this library, but #3 can solve this replacing at all the geofirestore-js library.