Files can have defined minimal php version for linting

If the system's PHP version doesn't match the rule then the file is skipped.
The rule must be on the first line in the file, right after the opening php tag

```php
<?php // lint >= 5.4
```
Check SkipLint parallel in one process
Merge branch 'fprochazka-feature/files-can-be-skipped'

Conflicts:
	src/Manager.php