Low level GeoJson implementation

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This is a request for either a rewrite or alternative implementation of the current GeoJson module found [here](https://github.com/mapbox/mapbox-java/blob/master/services-geojson). We need a high performance implementation that has a minimal memory footprint. The reasoning behind that is that geojson models should be scalable (eg. downstream we query the map for 1000 of features, the path currently taken to create those and the intermediate objects created for doing that isn't optimal atm).

Couple of thoughts to improve this:
- use primitive instead of objects where possible
- no need for AutoValue, implementation is based on a specification that doesn't change (often)
- if geojson models are immutable, use arrays instead of List
- limit method invocations & don't allocate memory if you can avoid it
- don't over abstract concepts if they can be expressed more simple

More information on performance tips [here](https://developer.android.com/training/articles/perf-tips.html)
RFC of GeoJSON can be found [here](https://tools.ietf.org/html/rfc7946).

cc @mapbox/android

Inizia esaminando l’implementazione attuale in services-geojson, quindi confronta la struttura dei relativi modelli con RFC 7946 e con i suggerimenti sulle prestazioni di Android collegati. Definisci come la riscrittura o l’alternativa misurerà l’impronta di memoria e le prestazioni per circa 1.000 features; il lavoro sarà considerato completato quando i modelli GeoJSON raggiungeranno gli obiettivi di scalabilità richiesti senza allocazioni o astrazioni non necessarie.

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