Classify polygon rings to distinguish inner polygon rings and multipolygons

[jfirebaugh]

This is a non-semver-major reimplementation of #33 that applies ring classification only in toGeoJSON. The structure of the return value of loadGeometry() is unchanged.

This is needed for mapbox/mapbox-gl-js#2586.

However, I can't get a GeoJSON Polygon with inner ring to round trip through a mapnik created vector tile. As the failing test here shows, it comes out with ring order indicating a multipolygon. cc @flippmoke @springmeyer @mourner.

[mourner]

What's the reason to keep it non-semver-major now that we have earcut in master + VT2? We could merge #33 instead and then eliminate duplicated classifyRings code from gl-js.

[jfirebaugh]

mapbox-gl-js depends now on vt-pbf, which would need a coordinated semver major release. Plus there are other things I'd want to consider for a semver major release (#34, #35), and I don't want to take them on right now. I'm already several levels down in a yak shave.

[mourner]

@jfirebaugh yeah, sounds good.

[springmeyer]

However, I can't get a GeoJSON Polygon with inner ring to round trip through a mapnik created vector tile. As the failing test here shows, it comes out with ring order indicating a multipolygon. cc @flippmoke @springmeyer @mourner.

Per chat confirmed this is not longer an issue.