Earth in Cube I (d3.js v4: working)

Fil has officially released support for polyhedral projections in d3.geo. So this is here just for historical reasons.

This is a reproduction of my earlier test for Earth in a Cube I using Fil's (not yet official) version of d3-geo.

Thanks to Philippe Rivière's great work on d3-geo (see his PR for clip-polygon), now general polyhedral projections are possible in D3 v4! (And let's not underestimate the great initial framework implementation by Jason Davies!)