Tutorial code not working for site_url and some inconsistencies in site_url

I started CodeIgniter recently and found few inconsistencies which I could not understand:

In this page:
https://www.codeigniter.com/user_guide/t...ction.html#

It says to use code:

$this->load->helper('url_helper');

But User guide for same at :
https://www.codeigniter.com/user_guide/h...elper.html

Says to use following code:
$this->load->helper('url');

Why two different versions?

Now comes my real problem:
$config['base_url'] = 'localhost/ci_host/'; // This was also not mentioned in tutorial.

My relevant code for application/views/news/index.php 
is following:

<?php echo "Base url: ". base_url('news');?>
<?php echo "Site url: ". site_url('news');?>
<?php echo "Slug: ". $news_item['slug'];?>
<p><a href="<?php echo site_url('news/'.$news_item['slug']); ?>">View article</a></p>

And out put for same is: 
Base url: localhost/ci_test/news
Site url: localhost/ci_test/index.php/news
Slug: new_item_1
Base url for slug: localhost/ci_test/news/new_item_1

View article

And "View article" takes me to following link:
http://localhost/ci_test/index.php/localhost/ci_host/index.php/news/new_item_1

But inspect on "View Article" shows following:

<a href="localhost/ci_host/index.php/news/new_item_1">View article</a>

Would be great to take me out of this.

Totally baffling me ...
My codeigniter base is located at: http://localhost/ci_test/