Config inspection

[elijaharita]

This ended up being a totally microscopic change, but it'll be extremely useful to library users. It is non-breaking change.

This saves the config into a private global variable upon applying it. You can call GetConfig() to read a copy of the config, and then it can be modified and re-applied using SetupLogging().

More info at #122. This solution is probably nicer than exposing configFromEnv(), because it reflects the actual current state of the logger, which could potentially change before configFromEnv() is next called.

[welcome]

Thank you for submitting this PR!
A maintainer will be here shortly to review it.
We are super grateful, but we are also overloaded! Help us by making sure that:

• The context for this PR is clear, with relevant discussion, decisions
  and stakeholders linked/mentioned.

• Your contribution itself is clear (code comments, self-review for the
  rest) and in its best form. Follow the code contribution
  guidelines
  if they apply.

Getting other community members to do a review would be great help too on complex PRs (you can ask in the chats/forums). If you are unsure about something, just leave us a comment.
Next steps:

• A maintainer will triage and assign priority to this PR, commenting on
  any missing things and potentially assigning a reviewer for high
  priority items.

• The PR gets reviews, discussed and approvals as needed.

• The PR is merged by maintainers when it has been approved and comments addressed.

We currently aim to provide initial feedback/triaging within two business days. Please keep an eye on any labelling actions, as these will indicate priorities and status of your contribution.
We are very grateful for your contribution!

[ribasushi]

This is great and so much simpler than I initially envisioned.