function featureFilter(geojson, fn) {
    const features = [];

    featureEach(geojson, feature => {
        if (fn(feature.properties)) {
            features.push(feature);
        }
    });
    return featureCollection(features);
}
Filter GeoJSON object using a filter function.
@param {Object} geojson - GeoJSON object
@param {Function} fn - Filter function that takes feature properties and returns
    a boolean value
@returns {Object} Filtered FeatureCollection