code: function Surface(app, options) {
    if (!(this instanceof Surface)) {
      return new Surface(app, options);
    }
  
    this.conf = setting(options);
  
    this.middleware(app);
    context(app, this);
  }
docs: Surface Constructor.
  @param {Object} app     koa().
  @param {Object} options Config object.
  @api public