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
```
Show properly message in Manager
Check SkipLint parallel in one process
Merge branch 'fprochazka-feature/files-can-be-skipped'

Conflicts:
	src/Manager.php
Fix skip-linting process if file not found
Fix in skip-linting bin