Method engine

packages/app/src/app.ts:226–230

* Register a template engine with extension

(ext: string, fn: TemplateFunc<RenderOptions>)

   * Register a template engine with extension
   */
  engine(ext: string, fn: TemplateFunc<RenderOptions>) {
    this.engines[ext] = fn

    return this
  }

  route(path: string): App {
    const app = new App()