Expose utility functions for plugin authors

[chris48s]

It might be useful to allow plugins to access some internals.

I think the obvious candidates to me would be

• https://github.com/chris48s/v8r/blob/main/src/output-formatters.js
• https://github.com/chris48s/v8r/blob/main/src/logger.js

That said, anything you expose here becomes public interface for semver purposes.

I think for the MVP plugins feature, the only thing I will expose is BasePlugin but this is a good place to collect thoughts and use-cases.