WIP:Feature manifold 3d

[hrgdavor]

Starting with a simple script that subtracts a sphere from a cube, performace difference is staggering (times are in ms).

segments	jscad	manifold 2.x	manifold 3.x
32	25.4	3.6	1.7
64	201.7	7.6	4.0
96	790	13	7
128	2098	20	12
192	10270	42	24

current url of branch while in progress https://3d.hrg.hr/jscad/manifold-test/#test.manifold.js