suspend fun TemplateEngine.renderAwait(context: JsonObject, templateFileName: String): Buffer
Render the template. Template engines that support partials/fragments should extract the template base path from the template filename up to the last file separator.
Some engines support localization, for these engines, there is a predefined key "lang" to specify the language to be used in the localization, the format should follow the standard locale formats e.g.: "en-gb", "pt-br", "en".
templateFileName - the template file name to use
handler - the handler that will be called with a result containing the buffer or a failure.