Takes polygon and face arrays and returns an OBJ string
var polygons2obj = require("polygons-to-obj");
var polygons = [[[x,y,z], [...]], [[x,y,z], [...]]];
var faces = [[[v1,v2,v3], [...]], [[v1,v2,v3], [...]]];
// Point to use as [0, 0, 0] origin for conversion
var origin = [0, 0, 0];
// Vertical offset to apply to points
var verticalOffset = 0;
// Z-axis is the vertical axis
var zUP = false;
var objStr = polygons2obj(polygons, faces, origin, verticalOffset, zUP);