The new dataclass ChangeNote helps with uncoupling the `_query.py` logic
and the `_format.py` logic from each other somewhat. In this case
one pull request can be turned into multiple change notes which might
appear in separate sections. This optional behavior allows to deal with
somewhat large or unfocused pull requests.

Long-term this step would also be necessary in case PyGitHub is replaced
with a GraphQl-based approach.

The new dataclass Contributor helps with uncoupling the `_query.py` logic
and the `_format.py` logic from each other somewhat.

Long-term this step would also be necessary in case PyGitHub is replaced
with a GraphQl-based approach.

Querying and formatting might generate warnings. Make sure that these
are printed before the generated notes.

This is nothing to fancy but it should catch unexpected changes in
our formatting logic and cover the happy path.

Co-authored-by: Stefan van der Walt <[email protected]>

Co-authored-by: Stefan van der Walt <[email protected]>

This syntax should hopefully be more robust than the previous one based
on the relatively common ":" character.

Attempts to make the usage of the new feature clearer.

Co-authored-by: Stefan van der Walt <[email protected]>