FeatureCollection.fromJson() should also accept a 'Reader' parameter

Currently a FeatureCollection can not be instantiated from a Reader.
The only function provided requires a String in JSON format as can be seen here.

Such approach is inefficient when reading larger files since the entire file content has to be read and stored in memory before it can be transformed into a FeatureCollection.
If a FeatureCollection could be instantiated from a Reader aswell, only parts of the read file would have to be stored in memory which makes this the more desirable approach in the presented situation.

As the used GSON library already enables the use of a Reader instead of a String, the implementation would be very simple and could look like this:

@Nullable
public static FeatureCollection fromJson(@NonNull Reader reader) { 
  GsonBuilder gson = new GsonBuilder();
  gson.registerTypeAdapterFactory(GeoJsonAdapterFactory.create());
  gson.registerTypeAdapterFactory(GeometryAdapterFactory.create());
  return gson.create().fromJson(reader, FeatureCollection.class);
}

阅读 services-geojson/src/main/java/com/mapbox/geojson/FeatureCollection.java 和现有的 fromJson(String) 入口点。使用所示的 Gson 适配器设置添加 Reader 重载，然后运行相关的项目测试，并确认 Reader 输入会生成 FeatureCollection，同时不改变现有的 String 行为。