Need a logging convention

We should write down guidelines for when to use `slog.Info*` vs `slog.Debug*` vs.`slog.Warn*` vs. `slog.Error*`

I'm very biased, but I think `Warn` is pointless (but I like V levels, so ...).

Proposed:

* use `Info` for things you always want to see
* use `Debug` for things you want only when "verbose" is enabled
* don't use `Warn`
* use `Error` for things that require human attention

A "normal" log should not include `Error` lines.