Pytest-fixture-order

Fixed
- Resolve `scopenum_function` ImportErrors with pytest 7.x (see [GH2](https://github.com/theY4Kman/pytest-fixture-order/issues/2); thank you, [last-partizan](https://github.com/last-partizan)!)

Changed
- Add compatibility for pytest versions up to ~6.0.0
- Transferred ownership to theY4Kman

Changed
- The `order(index)`, `early`, and `late` markers are now explicitly registered, to avoid warnings from pytest.
- The `combined` attribute is used to extract marker args/kwargs, to avoid warnings from pytest.
- Compatibility with pytest ~5.0.0 and ~5.1.0 is now tested.

Fixed
- Included README in package, for display on PyPI

Added
- Introduced `pytest.mark.order(index)`, `pytest.mark.early` (where `index = -1`), and `pytest.mark.late` (where `index = 1`) fixture markers to influence fixture evaluation order.