Add --format=silent

[unikitty37]

Is your feature request related to a problem? Please describe.

As there is no "watch" mode (see #18) I want to run organize from crontab every 5 minutes. Cron will cheerfully email any output to the user — good if there are errors, but --format=errorsonly does not actully only output errors — it also outputs the location of the config folder and the number of rules that succeeded or failed.

Describe the solution you'd like
I'd like to see --format=silent, which would only output error messages; if there were no errors, it outputs nothing at all.

Describe alternatives you've considered
I've considered trying some of the solutions in #18 but they add dependencies and seem to be rather too complicated to set up. Organize is described as an equivalent of Hazel on macOS, but Hazel watches file changes automatically and doesn't need all this fiddling around to do so.

I can add > /dev/null to the invocation in crontab, but this will trash any error output as well because organize outputs both its status messages and its error messages to stdout.

Running from cron is the only way I can think of that would be sufficiently hands-off.

Additional context
The UNIX philosophy is "succeed quietly, fail loudly", and it would be great if organize held to this — as well as putting the errors on stderr rather than stdout so they're where people expect them to be :)