Feature Request: Upon 429 or 503 status, retry after delay

A remoteStorage server (or a reverse proxy in front of it) may send a 429 or 503 status when too many requests are sent in a short time, especially if many of those requests are unauthorized or have invalid credentials.

It would be helpful for spec-check to pause for a short while, or for the duration of the Retry-After header, after receiving either of those status codes.