Proj::convert assumes 2D coordinates, and passes z: 0.0 into proj_sys (which handles 3D just fine).

This is insufficient for conversions to/from (e.g.) ECEF coordinates, where the z coordinate is critical even for locations on the ground.

Then need to access the private c_proj makes it impossible to define a trait with a minimally-modified convert method which takes a 3D point, passes all three values in/out of proj_sys, and returns a 3D point.

Some provision for 3D coords within this crate would be extremely helpful please :-)