added extra generator documentation

	 2) A mapping of keyword arguments, or

	 3) A 2-item object where item 0 matches (1) and item 1 matches (2)

	If the arguments resolve to an empty iterable or `None` no tests will be 

	generated for the test case, although the generator will still be available 

	for sub-classed test cases. (Note: this only makes sense when using named

	arguments.)

	Examples:

	  Pass an arguments list directly to the decorator, the same tests will be 

	  generated in all subclassed test cases as well:

	  ```

	  class TestCase(unittest.TestCase, metaclass=TestGeneratorMeta):

	          # run test with a & b...

	  ```

	  Pass the name of the arguments list to the generator, the tests will only 

	  be generated for classes that define the named list:

	  ```

	  class TestCase(unittest.TestCase, metaclass=TestGeneratorMeta):

	          # run test with a & b...

	  ```

	  Pass positional and keyword arguments together:

	  ```

	  class TestCase(unittest.TestCase, metaclass=TestGeneratorMeta):

	      def some_test(self, a, b, type=None):

	          # run test with a & b...

	  ```

	  A test generator for use by subclasses ONLY, no tests generated in the 

	  class in which it is defined:

	  ```

	  class TestCase(unittest.TestCase, metaclass=TestGeneratorMeta):

	      some_test_args = None

	      @test_generator('some_test_args')

	      def some_test(self, a, b):

	          # no tests in this TestCase, but subclassed TestCases may 

	          # override `some_test_args` to generate tests with this function.

	  ```

	"""

	def __init__(self, values=None):