Add Dart support

samples/client/petstore/dart/test/tests.dart

@@ -0,0 +1,16 @@
+library tests;
+
+import 'dart:async';
+import 'package:http/http.dart';
+import 'package:guinness/guinness.dart';
+import 'package:swagger/api.dart';
+
+part 'pet_test.dart';
+part 'store_test.dart';
+part 'user_test.dart';
+
+main() {
+  testPetApi();
+  testStoreApi();
+  testUserApi();
+}