- ⚠️ Breaking: `flatbush(...)` should now be `new Flatbush(...)`.
- Add optional `data` constructor argument for reconstructing an index after transferring.
- Use ES syntax in the exported module (doesn't affect node/browser builds).
- Expose `numItems`, `nodeSize`, `ArrayType`, `minX`, `minY`, `maxX`, `maxY` properties.
- Avoid worst case performance when data is already hilbert-sorted.