Set up the command-line options.

def setup_parser():
    '''Set up the command-line options.'''
    parser = argparse.ArgumentParser(description='Add random pages to existing site.')
    parser.add_argument('-d','--directory', action='store', default= os.getcwd(),
                                 help='Site directory (must be a valid s2 structure).')
    parser.add_argument('-n','--number', action='store', type=int, default = 20,
                                 help='Number of pages to generate.')

    return parser