Backports-datetime-fromisoformat

* Switched to `pyproject.toml`
* Switched to `pytest` as a test runner
* Added wheel builds

* Backport the logic from Python 3.11's `fromisoformat` methods, instead of Python 3.7's, [22](https://github.com/movermeyer/backports.datetime_fromisoformat/pull/22)
* Adds support for a wider portion of the ISO 8601 specification
* Backports are now applied to Python < 3.11, instead of only Python < 3.7

1.x.x

* Made FixedOffset objects picklable/copyable (Solves 12, Thanks jappievw)

0.x.x

* Fixed build issue that impacted certain installations (10, Thanks rlyons)

* Initial release