How to handle rate-limits on error?

[Tobjoern]

When calling the api via app.api(x, y, z), and an error occurs due to rate limiting (https://developers.facebook.com/docs/graph-api/overview/rate-limiting),
one should be able to inspect the X-App-Usage or X-Ad-Account-Usage header, but I don't see them in the headers.

[dantman]

Try getAppUsage to get the last X-App-Usage. I don't think the code currently handles Ad-Account-Usage.