add doctests

    If 'filename' is a directory, then create that directory. If 'filename' is

    an ordinary file, then create the directory that would contain the file.

    Examples

    --------

    >>> import os

    >>> dirname = os.path.join("data", "tests", "test_util")

    >>> create_directory(f"{dirname}") # creates 'tests' if did not exists

    >>> create_directory(f"{dirname}/") # creates 'test_util'

    >>> create_directory(f"{dirname}/foo") # creates 'dirname'

    >>> create_directory(f"{dirname}/foo/") # creates 'foo'

    >>> create_directory(f"{dirname}/bar/test.dat") # creates 'bar'

    >>> assert os.path.exists("data/tests")

    >>> assert os.path.exists("data/tests/test_util")

    >>> assert os.path.exists("data/tests/test_util/foo")

    >>> assert os.path.exists("data/tests/test_util/bar")

    """

    if not os.path.isdir(filename):

        filename = os.path.dirname(filename)