Why is this package needed?

I am not sure how your code makes a difference against using the standard JSONFormatter like this:
```golang
logrus.SetFormatter(&log.JSONFormatter{
    FieldMap: logrus.FieldMap{
        logrus.FieldKeyTime:  "time",
        logrus.FieldKeyLevel: "severity",
        logrus.FieldKeyMsg:   "message",
    },
})
```
Could you please elaborate?
