ActiveJob automatic retries

I’ve written an external gem for adding automatic retry support to ActiveJob, activejob-retry. It supports constant/variable backoff, and make it super easy to define a custom backoff strategy. At present it supports Backburner, DelayedJob, Que, and Resque, and could potentially support Sidekiq too. Feels like this could be something ActiveJob supports out of the box in a future version, but thought I’d check here before doing the work to turn it into a PR onto Rails.