GeoJSON point clustering

[mourner]

Closes #320, a work in progress. cc @jfirebaugh

• add Supercluster type to urlOrGeoJSON variant
• instantiate Supercluster index in GeoJSONSource::Impl setGeoJSON if cluster is true in options and use it in createTile
• see if we can avoid adding geojson to include paths and public headers
• bump supercluster.hpp and kdbush.hpp to fix compiler warnings in iOS
• fix cluster wrapping near the date line
• make sure all platforms are building
• clean up the code
• un-ignore clustering test in render suite and make sure it passes
• review by @jfirebaugh
• rebase and add [core] prefix to commits
• rejoice!

[mention-bot]

@mourner, thanks for your PR! By analyzing the annotation information on this pull request, we identified @jfirebaugh, @yhahn and @boundsj to be potential reviewers

[mourner]

OK, clustering now seems to be working!

[jfirebaugh]

Let's keep this header file and keep using the GeoJSON symbol, but change the definition to:

namespace mbgl {

using GeoJSON = mapbox::geojson::geojson;

} // namespace mbgl

This follows a convention established by mbgl::Geometry, mbgl::Feature, etc. It keeps the naming conventions within the project more consistent, and allows for definition changes (like this one) to happen with minimal changes to downstream code.

[mourner]

Sure, will do.

[mourner]

The tests passed, woohoo! Now what's left is rebase + cleanup + merge.

[1ec5]

Should there be corresponding changes in macos.xcodeproj?

[mourner]

Maybe — let me add them. I wonder why it's not caught by the builds though.

[leekuo]

Any idea when this will make it into the iOS SDK release?

[1ec5]

@leekuo, this functionality is now in ios-v3.4.0-alpha.1. Please note the caveats in #320 (comment).