Add auto-update functionality

[rcloran]

Fixes #102

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[rcloran]

It's also not clear from the issue whether a prompt like this is what's wanted, or rather integration with the myriad cron-like systems out there, which would be quite a lot of work.

If what I've written isn't desired in znap, I won't be upset at all, happy to abandon it. I'd written it anyways for myself, since this is the functionality that I wanted on my machines.

[rimmer]

Looking forward to have it merged

[marlonrichert]

It's also not clear from the issue whether a prompt like this is what's wanted, or rather integration with the myriad cron-like systems out there, which would be quite a lot of work.

I think it's a bad idea to check on each shell startup whether to update. I would rather solve it in way that's similar to how git maintenance does it. See https://git-scm.com/docs/git-maintenance#Documentation/git-maintenance.txt---schedulerautocrontabsystemd-timerlaunchctlschtasks and the sections below it.

Are you interesting in updating your pull request to provide the initial framework for this? You don't need to implement support for all possible cron-like systems immediately. Just start with one, like crontab or launchctl, and we can add the rest later. Just keep it simple.

Thanks for contributing! 🙂