Feature request: give up early on 505, 506, 510, and 511

In addition to 501, these errors seem permanent as well:
```go
http.StatusHTTPVersionNotSupported // 505 HTTP Version Not Supported
http.StatusVariantAlsoNegotiates // 506 Variant Also Negotiates
http.StatusNotExtended // 510 Not Extended
http.StatusNetworkAuthenticationRequired // 511 Network Authentication Required
```
Perhaps we should skip the retry logic when we see one of them?

PS: I'm not sure about `http.StatusLoopDetected` (508 Loop Detected). Maybe we should include that as well.