- Breaking change for `addJavaScriptHandler` method
-`addJavaScriptHandler` method can return data to JavaScript using `Promise`[#46](https://github.com/pichillilorenzo/flutter_inappbrowser/issues/46)
- added `flutterInAppBrowserPlatformReady` JavaScript event to wait until the platform is ready [#64](https://github.com/pichillilorenzo/flutter_inappbrowser/issues/64)