remove build artifacts

def clean():
    """remove build artifacts"""
    shutil.rmtree('{PROJECT_NAME}.egg-info'.format(PROJECT_NAME=PROJECT_NAME), ignore_errors=True)
    shutil.rmtree('build', ignore_errors=True)
    shutil.rmtree('dist', ignore_errors=True)
    shutil.rmtree('htmlcov', ignore_errors=True)
    shutil.rmtree('__pycache__', ignore_errors=True)