Handle rate limiting for openrss.org

[brentsimmons]

Pay attention to 429 status code and the Retry-After header.

[DamonHD]

May I suggest treating it and Cache-Control max-age the same, to maintain a don't-update-before internal date?

Slow-updating feeds really don't need to be checked every hour if they tell you to cache things or go away for several hours!

And you'll help save some battery life and data charges and carbon emissions for client and server too... B^>

Rgds

Damon