New option: run_once, and removed skip_waiting

[mpl]

• new default behaviour: an update check is always attempted right from the start, regardless of check_frequency value.
• run_once: controls whether we exit right after the initial update check.
• skip_waiting: removed

Fixes #6

[mpl]

@damdo How do you work in the way of tests and CI? Are there going to be github actions running for this?
Disclaimer: I'm doing this PR on my mac, so I haven't tried building it or testing it (yet).

[damdo]

Thanks @mpl the PR looks good to me, added two little nitpicks but nothing blocking.

[damdo]

@damdo How do you work in the way of tests and CI? Are there going to be github actions running for this?
Disclaimer: I'm doing this PR on my mac, so I haven't tried building it or testing it (yet).

At the moment I use a very rough make target that I have checked in here: https://github.com/gokrazy/selfupdate/tree/e2e-test
The plan is to finish off gokrazy/tools#62 and then turn this into a go e2e test that we can run on GH actions.

[mpl]

@damdo do you prefer the --amend+push force flow (I'm used to it because of reasons), or do you want distinct commits on the PR, and we squash them all at merge time?

[damdo]

Fine to amen + force push :) thanks for asking @mpl

[damdo]

Thanks @mpl will do a manual test and add my review