RFC: chained retry rulesets

[mharrisb1]

Request for comment (RFC) on potential new feature:

This may already be possible but I thought of this as an alternative or extension of #22

To breakdown complex retry ruleset maybe there could be a way to chain multiple rules so the user can separate concerns for different rulesets.

An example would be I want to retry only once on 4XX status codes but retry 10 times with 5XX status codes. Those are 2 different rules that I would want to combine to a single ruleset.

Not sure what the API would look like for this.

[will-ockmore]

For this and the last example, we could add a guide to the docs on how to implement very complex retry strategies. For this one like the other, my preference would be to demonstrate subclassing Retry directly. An example could even demonstrate how adding additional attributes to the class could simplify some of these more complex scenarios - like splitting the count into multiple variables by status code.