fix #626, add AMD module format and make it default

lib/runtime/run.js

-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-var fs = require('fs');
-var vm = require('vm');
-
-function __load(path) {
-  var data = fs.readFileSync(path);
-  var script = vm.createScript(data.toString(), path);
-  script.runInThisContext();
-}
-
-var args = process.argv.slice(2);
-var argc = args.length;
-
-for (var i = 0; i < argc-1; ++i) {
-  __load(args[i]);
-}
-
-var main = vm.createScript(args[argc-1] + '.main()', 'main');
-main.runInThisContext();