[FEAT] New rule no-surrounding-whitespace

[KamiKillertO]

This PR adds the new rule no-surrounding-whitespace proposed in issue #148.
This rule forbids the presence of whitespaces before or after a text node.
Here's a list of valid/invalid snippets.

VALID snippets:

<h1>Lorem ipsum</h1>

<p><strong>Lorem</strong> ipsum</p>

<p><!-- comment --><strong>Lorem</strong> ipsum</p>

<div>
    <p>Lorem ipsum dolor sit amet...</p>
</div>

<div>
    <p>
        Lorem ipsum dolor sit amet...
    </p>
</div>

<div>
    <p>
        <!-- comment -->
        Lorem ipsum dolor sit amet...
        <!-- comment -->
    </p>
</div>

<div></div>

INVALID snippets:

<h1> Lorem ipsum</h1>

<h1>Lorem ipsum   </h1>

<h1> Lorem ipsum </h1>

<p> <strong>Lorem</strong> ipsum</p>

<p> <!-- comment --><strong>Lorem</strong> ipsum</p>

<div> </div>

[acalvo]

Great! 🥳

Can you add this one to the test suite?

<div>
  <p>Lorem ipsum</p>
</div>

It's throwing an error in my tests and it shouldn't.

[KamiKillertO]

@acalvo it's fixed

[acalvo]

Works like a charm now!

It's OK for me, can be merged. Thanks a lot!