Attach argument parser for action specific options.

    Arguments
    ---------
    module : module
        name of module to extract action from
    parser : argparser
        argparser object to attach additional arguments to
    method : str
        name of method (morris, sobol, etc).
        Must match one of the available submodules
    opts : list
        A list of argument options to parse

    Returns
    ---------
    subargs : argparser namespace object

def parse_subargs(module, parser, method, opts):
    '''Attach argument parser for action specific options.

    Arguments
    ---------
    module : module
        name of module to extract action from
    parser : argparser
        argparser object to attach additional arguments to
    method : str
        name of method (morris, sobol, etc).
        Must match one of the available submodules
    opts : list
        A list of argument options to parse

    Returns
    ---------
    subargs : argparser namespace object
    '''
    module.cli_args(parser)
    subargs = parser.parse_args(opts)
    return subargs