UITableView在Plain类型下，HeaderView和FooterView不悬浮和不停留的方法

既可以让headerView不悬浮在顶部，也可以让footerView不停留在底部。

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    CGFloat sectionHeaderHeight = 40;
    CGFloat sectionFooterHeight = 10;
    CGFloat offsetY = scrollView.contentOffset.y;
    if (offsetY >= 0 && offsetY <= sectionHeaderHeight)
    {
        scrollView.contentInset = UIEdgeInsetsMake(-offsetY, 0, -sectionFooterHeight, 0);
    }else if (offsetY >= sectionHeaderHeight && offsetY <= scrollView.contentSize.height - scrollView.frame.size.height - sectionFooterHeight)
    {
        scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, -sectionFooterHeight, 0);
    }else if (offsetY >= scrollView.contentSize.height - scrollView.frame.size.height - sectionFooterHeight && offsetY <= scrollView.contentSize.height - scrollView.frame.size.height)
    {
        scrollView.contentInset = UIEdgeInsetsMake(-offsetY, 0, -(scrollView.contentSize.height - scrollView.frame.size.height - sectionFooterHeight), 0);
    }
}