Add one more log level (notice/verbose?)

When writing command line programs, I often find myself wanting two distinct "info"-like log levels: one for regular output and one when a --verbose flag is requested by the user. Then implementing --verbose is simply a matter of changing the log level. I think the Debug level is wrong for this purpose because it's oriented towards developers, whereas --verbose is typically intended for troubleshooting by users.

There would be two ways to go about it:

• Warn > Notice > Info > Debug
• Warn > Info > Verbose > Debug

I realize that similar things have been requested before (#240, #229), but I think my use case is actually a quite helpful one.

If your consideration is to keep the number of built-in log levels low, I actually don't find a distinct Trace level to be useful; seems like debug output to me. But perhaps other people do? What was the justification for that in the first place? :)

The issue names no files or tests; start by reviewing the existing log-level API and the earlier discussions in #240 and #229. First resolve whether Notice or Verbose is wanted and its ordering, then define acceptance criteria with maintainers; the work is done only after an agreed API and coverage for the new level.