This is a partial port of the geomesa-z3 package from [geomesa](https://github.com/locationtech/geomesa).
It is also a partial port of [sfcurve](https://github.com/locationtech/sfcurve/).
This library has 2D and 3D z-order curves that index points as well as 2D and 3D
extended z-order curves for indexing objects by bounding box.