add support for skipping parametrized unit tests
add support for skipping parametrized unit tests

Example:

    @parametrize
    class test(TestCase):

      @parametrize.skip_if(lambda nprocs: nprocs > 1 and not hasattr(os, 'fork'), 'nprocs>1 not supported on this platform')
      def check(self):
        ...

    test(nprocs=1)
    test(nprocs=2)

wijnandhoitinga/nutils,CVerhoosel/nutils,nutils/nutils,joostvanzwieten/nutils