Parse command-line arguments.

def process_args():
    """ 
    Parse command-line arguments.
    """
    parser = argparse.ArgumentParser()

    parser.add_argument('-I', type=str,
                        metavar='<Include directory>',
                        action='append',
                        help='Directory to be searched for included files')
                        
                        
    parser.add_argument('lems_file', type=str, metavar='<LEMS file>', 
                        help='LEMS file to be simulated')
                        
    parser.add_argument('-nogui',
                        action='store_true',
                        help="If this is specified, just parse & simulate the model, but don't show any plots")
                        
    parser.add_argument('-dlems',
                        action='store_true',
                        help="If this is specified, export the LEMS file as "+dlems_info)
    
    return parser.parse_args()