code: function markerHandler(req, res, next) {
    const start = Date.now();
    const { params } = req;
  
    return Promise.try(() => {
      if (params.color.length !== 3 && params.color.length !== 6) {
        throw new Err('Bad color').metrics('err.marker.color');
      }
      let isRetina;
      if (params.scale === undefined) {
        isRetina = false;
      } else if (params.scale === '2') {
        isRetina = true;
      } else {
        throw new Err('Only retina @2x scaling is allowed for marks').metrics('err.marker.scale');
      }
  
      return makizushi({
        base: params.base, // "pin"
        size: params.size, // s|m|l
        symbol: params.symbol, // undefined, digit, letter, or maki symol name - https://www.mapbox.com/maki/
        tint: params.color, // in hex - "abc" or "aabbcc"
        retina: isRetina, // true|false
      });
    }).then((data) => {
      core.setResponseHeaders(res);
      res.type('png').send(data);
      core.metrics.endTiming('marker', start);
    }).catch(err => core.reportRequestError(err, res)).catch(next);
  }
docs: Web server (express) route handler to get a marker icon
  @param req request object
  @param res response object
  @param next will be called if request is not handled