function GeoJSON(params) {
    Transform.call(this, null, params);
  }
Consolidate an array of [longitude, latitude] points or GeoJSON features
into a combined GeoJSON object. This transform is particularly useful for
combining geo data for a Projection's fit argument. The resulting GeoJSON
data is available as this transform's value. Input pulses are unchanged.
@constructor
@param {object} params - The parameters for this operator.
@param {Array<function(object): *>} [params.fields] - A two-element array
  of field accessors for the longitude and latitude values.
@param {function(object): *} params.geojson - A field accessor for
  retrieving GeoJSON feature data.