Return version string.

def version():
    """Return version string."""
    with open(os.path.join(os.path.abspath(os.path.dirname(__file__)),
                           'pep8radius',
                           'main.py')) as input_file:
        for line in input_file:
            if line.startswith('__version__'):
                return parse(line).body[0].value.s