Add support for WaitTime and MaxWaitTime for retries

[bak1an]

Currently client does not expose a way to configure wait times for retry, only conditions and retry count are configurable -

resty/request.go

Line 430 in 90b37fd

}, Retries(r.client.RetryCount), RetryConditions(r.client.RetryConditions))

We need to make wait times configurable as well, default 100ms wait time is too little in my case.

I can provide a pull request for this if the issue is valid

[bak1an]

I am also wondering why retry config functions and Backoff function were made public in https://github.com/go-resty/resty/blob/master/retry.go ?

Was the idea to let user wrap client.Execute(...) into an anonymous function and pass it to Backoff?

[jeevatkm]

@bak1an Configurable option is good. Feel free to send PR.

Yes, that was my thought when I made those as public.

[bak1an]

Great, will be on it during the week