V2

[flowchartsman]

I kind of don't like that I have to do something like

rp := retry.NewRetrier(...)
err := rp.Run(func()error{
    // ...
})

The method should be Retry() or RetryWithContext(), because that's what it's doing. Alas, Go modules tell us this is a breaking change, so it would mean V2. I'd prefer to improve more than that, so I'm opening this issue to track things that could be done better (#7 certainly didn't feel great), so feel free to drop any suggestions here, and I'll close this ticket when I drop a V2. Or maybe I'll just make a new module, who knows!