Example:
        >>> # DISABLE_DOCTEST
        >>> from utool.util_cplat import *  # NOQA
        >>> import utool as ut
        >>> dpath = ut.ensure_app_cache_dir('utool')
        >>> assert exists(dpath)

def ensure_app_cache_dir(appname, *args):
    """
    Example:
        >>> # DISABLE_DOCTEST
        >>> from utool.util_cplat import *  # NOQA
        >>> import utool as ut
        >>> dpath = ut.ensure_app_cache_dir('utool')
        >>> assert exists(dpath)
    """
    import utool as ut
    dpath = get_app_cache_dir(appname, *args)
    ut.ensuredir(dpath)
    return dpath