Wrap raw geometries in feature collections

Nobody has claimed this yet.

This library assumes that a GeoJSON object can only contain Feature and FeatureCollection objects, but it can also contain raw Geometry objects such as Point or MultiPolygon:

```json
{
"type": "Point",
"coordinates": [0, 0],
}
```

We haven’t been running into these geometries because we rely on [geojson-normalize](https://github.com/mapbox/geojson-normalize/) to wrap them in FeatureCollections via [static-map-string-format](https://github.com/mapbox/static-map-string-format). We should either make geojson-normalize a dependency of this library or duplicate its functionality here.

/cc @bsudekum

Start by inspecting the JavaScript entry points and dependency configuration in simplespec-to-gl-style, then compare the wrapping behavior provided by geojson-normalize and static-map-string-format. The work is done when raw GeoJSON geometries such as Point and MultiPolygon are accepted as FeatureCollections, with coverage for the supported input forms.

Written by the indexing model from the issue text.