Added i18n skeleton API for message_formatting

tests/lib/i18n/message_format_test.dart

+/**
+ * Copyright (c) 2012, 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.
+ */
+
+#library('message_format_test');
+
+#import('../../../lib/i18n/message_format.dart');
+#import('../../../lib/unittest/unittest.dart');
+
+/**
+ * Tests the MessageFormat library in dart.
+ */
+
+main() {
+  test('Message formatting', () {
+    var msg_format = new MessageFormat(
+      'Message telling user how many emails will be sent.',
+      '''{NUM_EMAILS_TO_SEND, plural,
+          =0 {unused plural form}
+          =1 {One email will be sent.}
+          other {# emails will be sent.}}''');
+    // TODO(efortuna): Uncomment when functioning correctly.
+    //Expect.stringEquals('5 emails will be sent.',
+    //                    msg_formatter.format({'NUM_EMAILS_TO_SEND' : 5})); 
+  });
+}