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

Source/node_modules/core-js/modules/es6.number.is-safe-integer.js

@@ -0,0 +1,10 @@
+// 20.1.2.5 Number.isSafeInteger(number)
+var $export = require('./_export');
+var isInteger = require('./_is-integer');
+var abs = Math.abs;
+
+$export($export.S, 'Number', {
+  isSafeInteger: function isSafeInteger(number) {
+    return isInteger(number) && abs(number) <= 0x1fffffffffffff;
+  }
+});