[Feature] Diff output configurable

[Jibbarth]

Q	A
Bug fix?	yes
New feature?	yes
Fixed tickets	#...

👋

This PR to improve display for diff.

By default, I add 1 line of context around the diff. I also improve the default display by removing some empty lines.

Before:

After:

But, now, we can configure the diff context around.

In phpinsights.php, add the following line:

<?php

return [
    // ...
    'diff_context' => 3,
]

Output:

While testing, I noticed that when configuration file has some invalid options, the output was really ugly:

I rework a little this part to improve output when there is an invalid configuration:

[Jibbarth]

@50bhan do you want to review this one ?

[50bhan]

@Jibbarth LGTM 👍

Thank you for this. The errors on the wrong config options were really annoying 😄