Merge pull request #373 from ev-br/skip_xfails

ENH: add ARRAY_API_TESTS_XFAIL_MARK to turn xfails into skips

Improved values testing for elementwise and operators tests.

array-api-tests version 2022.1 (first version)

Add versioneer

This will let us tag versions and array_api_tests.__version__ will
automatically be set to it.

This also supports setup.py, but we don't have one right now (I'm not sure if
it would be useful).