api: Use exponential backoff in call_on_each_event.#586

neiljp wants to merge 3 commits intozulip:mainzulip/python-zulip-api:mainfrom

neiljp:2020-04-exponential-backoff-in-call_on_each_eventneiljp/python-zulip-api:2020-04-exponential-backoff-in-call_on_each_eventCopy head branch name to clipboard