support adding `FeatureCollection`s - closes #65
support adding `FeatureCollection`s - closes #65

mapbox/gl-draw,mapbox/gl-draw,mapbox/mapbox-gl-draw,kiRach/mapbox-gl-draw,drewbo/mapbox-gl-draw,drewbo/mapbox-gl-draw,mapbox/mapbox-gl-draw,kiRach/mapbox-gl-draw