possibly prepend commands on registration instead of appending them

[adaraiseh]

prepend function:

struct cli_command *cli_register_command_core(struct cli_def *cli, struct cli_command *parent, struct cli_command *c) {
    if (!c) return NULL;

    c->parent = parent;

    // Build the 'full command name'
    if (!(c->full_command_name = cli_int_command_name(cli, c))) {
        cli_free_command(cli, c);
        return NULL;
    }
    /*
     * Prepend the command 'c' to the beginning of the list.
     * If 'parent' is not NULL, prepend to 'parent->children'.
     * Otherwise, prepend to 'cli->commands'.
     */
    if (parent) {
        c->next = parent->children;
        if (parent->children) {
            parent->children->previous = c;
        }
        parent->children = c;
    } else {
        c->next = cli->commands;
        if (cli->commands) {
            cli->commands->previous = c;
        }
        cli->commands = c;
    }

    c->previous = NULL; // 'c' is now the first node, so its previous is NULL
    return c;
}