Polygonize a Raster

[Raf]

This works for writing. Unfortunately GeoJSON doesn’t handle a Vector of geometries, so wrap pol with a GeometryCollection

GeoJSON.write("test.json", GeometryOps.GeoInterface.GeometryCollection(pol))

We should with make GeoJSON handle a Vector, or make GeometryOps return a GeometryCollection or just MultiPolygon from polygonize. Its very early days for GeometryOps. It should be accurate and its insanely fast, but workflows like this are not polished yet.

Then read will get you a GeometryCollection back:

julia> GeoJSON.read("test.json")
GeometryCollection with 1 2D geometries

Issue here:

`polygonize` should return a `MultiPolygon`, not a `Vector` of `Polygon`

Allow `write` for ` Vector` or even other itererables of geometries.