code: function (opts, baseMeta) {
      // Stash singleton logger for all requests.
      var singleton = new winston.Logger(opts);
      var meta = _.extend({ type: "unhandled_error" }, baseMeta);
  
      return function (err, req, res, next) {
        // Create logger and add objects.
        (new Log(_.extend({ singleton: singleton }, opts), meta))
          .addReq(req)
          .addRes(res)
          .addError(err)
          .error("unhandled error");
  
        // Pass to underlying Express handler.
        next(err);
      };
    }
docs: `error(opts, baseMeta)` - Express error middleware
  
  Creates a middleware function for Express. Integration:
  
  ```
  app.use(winMid.error({
  transports: [ new (winston.transports.Console)({ json: true }) ]
  }, { foo: "bar" }));
  ```
  
  @param {Object} opts     Winston logger options.
  @param {Object} baseMeta Metadata for log statements.
  @api public