First support for md extensions; Package all needed dependencies in the repo

Source/node_modules/core-js/modules/es6.math.cbrt.js

@@ -0,0 +1,9 @@
+// 20.2.2.9 Math.cbrt(x)
+var $export = require('./_export');
+var sign = require('./_math-sign');
+
+$export($export.S, 'Math', {
+  cbrt: function cbrt(x) {
+    return sign(x = +x) * Math.pow(Math.abs(x), 1 / 3);
+  }
+});