v1.6.0 - empty lines at the file header

As described in #67 and implemented in #76, from now we are enforcing a proper blank lines in every file "head section".

With these changes this:

<?php
declare(strict_types=1);
namespace Test;
class Test
{
}

will be fixed into:

<?php

declare(strict_types=1);

namespace Test;

class Test
{
}