Added autoCastResponse option to RestApi and all Method annotations (default : true)

Added auto_cast_response to builder options.

• Users can specify this in build.yaml as global default

  targets:
    $default:
      sources: ["lib/**"]
      builders:
        retrofit_generator|retrofit:
          enabled: true
          options:
            auto_cast_response: true
  

Added @Extra to pass extra options to dio requests, response, transformer and interceptors.

Example :

@http.POST('/path/')
@dio.Extra({'my_key':'my_value'})
Future<String>> myMethod();

Fixed general dart style and code conventions

Automatically null check with ArgumentError.checkNotNull for required parameters

Now SuperClasses can use forwarding/redirecting constructors instead of static instance() method

Example :

@RestApi(baseUrl: "https://httpbin.org/")
abstract class RestClient {
    /// Forwarding constructor
    factory RestClient([Dio dio]) = _RestClient;
}