Move MetaWarning classes into new cli module

[Pennycook]

Related issues

Part of #36, #96.

The CLI is the least well-tested part of Code Base Investigator, because its legacy implementation lived outside of the codebasin/ package and was therefore difficult to test. Refactoring common CLI functionality into a dedicated module, using functions with well-defined interfaces, will make this functionality more reliable.

Proposed changes

• Move Formatter, MetaWarning and WarningAggregator into a new cli module.
• Add missing docstrings.
• Add unit tests for Formatter, MetaWarning and WarningAggregator.

[laserkelvin]

Not sure if it's just me, but the naming of this module doesn't seem to really fit its contents?

It's called cli.py but it contains logging stuff, and if we're moving things around, would it make sense to name it something that maps better? (log_utils.py?)

Otherwise, refactors and new tests look good to me

[Pennycook]

Ah, I can see the confusion. I'll explain my logic, and you can tell me if it makes sense 😆.

The thinking behind this "cli" module was that it would contain things that were only useful for the user-facing command-line interface, but which might be shared across commands (e.g., the Formatter is currently used by both codebasin and cbicov).

I was basically looking for a way to separate things that we use to build the user-facing CLI from the modules and interfaces that we (eventually) want people to be able to use when importing the codebasin package into another script.

Maybe it would be better to have this as something like a cli package, containing a logging.py? Or an _internal package containing a logging.py? I'm definitely open to suggestions here.