Pytest-reporter

- Fix pytest-xdist
- Replace use of pkg_resources

* Save reports as UTF-8

* Support pytest < 6.0 again

* Use pytest_warning_recorded instead of pytest_warning_captured
* Remove function_context fixture

* Add support for pytest-xdist
* The `tests[].phases[].call` item is now optional (not available when using pytest-xdist)
* Add `tests[].phases[].sections` item with only the sections captured for this phase
* Add `items` dictionary

* Update documentation
* Prevent missing status from crashing report