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

Source/node_modules/core-js/modules/es7.string.at.js

@@ -0,0 +1,15 @@
+'use strict';
+// https://github.com/mathiasbynens/String.prototype.at
+var $export = require('./_export');
+var $at = require('./_string-at')(true);
+var $fails = require('./_fails');
+
+var FORCED = $fails(function () {
+  return '𠮷'.at(0) !== '𠮷';
+});
+
+$export($export.P + $export.F * FORCED, 'String', {
+  at: function at(pos) {
+    return $at(this, pos);
+  }
+});