Use require for poly-decomp

[liabru]

Use require for poly-decomp. But do not include poly-decomp in the build for Matter.js. Ensure that this also works in a browser, where poly-decomp is required separately.

[donaldpipowitch]

I use it with webpack in this way for now:

import decomp from 'poly-decomp';
import { Engine, World, Bodies, Svg, Vertices } from 'matter-js';

window.decomp = decomp;

(By the way: Using webpack gives a warning This seems to be a pre-built javascript file. (build/matter.js 32:479-486). I don't know if this can make problems in Browserify/webpack environments, because there seems to be a require fallback.)

[liabru]

Solved as of c72a9d0.