Add form builder (#235)

* add form builder

* cover VariImage

* test for closing errors

* simplify tests

* add audio api test coverage

* don't leak authToken when printed

* rename api->client

* fix test

config.go

@@ -64,3 +64,7 @@ func DefaultAzureConfig(apiKey, baseURL, engine string) ClientConfig {
 		EmptyMessagesLimit: defaultEmptyMessagesLimit,
 	}
 }
+
+func (ClientConfig) String() string {
+	return "<OpenAI API ClientConfig>"
+}