Adding middleware utility.
Preparation for unittests.
Adding request_test.dart.
Minor changes.
Adding response_test.dart.
Adding type_matcher.dart.
Adding ws_request_test.dart.
Adding MockRequest class.
Check if middleware is empty.
Cannot close() server if server isDown.
Adding factory constructor to Server class.
Adding sink.add() to non-websocket case.
Minor deletion.
Adding server_test.dart.