Pytest-nunit

* Docstrings of nodes (functions) are set as the label for TestCase elements (contribution by mikeattara)
* Pytest -k keyword filters are added to the test run filter element under ``name``.
* Pytest -m marker filters are added to the test run filter element under ``namespace``.
* Any path filters are added to the test run filter element under ``test``.
* Each Python module containing tests is now a separate ``test-suite`` element, instead of having one large suite
* Docstrings of modules are set as the label for TestSuite elements

* Added user domain (contribution by williano)
* Added tests and help for xdist execution (contribution by mei-li)
* Dynamically use the keyword list when generating schema to avoid reserved word collision (contribution by gerhardtdatsomor)
* Add method names, classnames and module names to output (contribution by adekanyetomie)
* Added locale and uiculture properties to runtime output (contribution by terrameijar)
* Added ``nunit_attach_on`` INI option to control when attachments are included in test cases.

* Added ``--nunit-prefix`` option.

* First stable release