Re-introduce delete(all) / retry(all) from #37

Everything is pretty much the same as in original pull request.
Hopefully now a little bit cleaner and of course updated to the latest.
Fix typo in CHANGELOG.md.
Merge pull request #59 from rjackson/patch-1

Fix typo in CHANGELOG.md.
Merge pull request #56 from spectator/retry_jobs_take2

Re-introduce delete(all) / retry(all) from #37
manually apply #64