code: public Yoke engine(@NotNull Engine engine) {
          engine.setVertx(vertx);
          engineMap.put(engine.extension(), engine);
          return this;
      }
docs: Adds a Render Engine to the library. Render Engines are Template engines you
  might want to use to speed the development of your application. Once they are
  registered you can use the method render in the YokeResponse to
  render a template.
  
  @param engine    The implementation of the engine