Align FilterIterator::accept() method signatures

[dereckson]

Fixes #11.

[theseer]

While the proposed fix makes perfect sense, its syntax is not PHP 5.3.1 compliant ;)

The DirectoyScanner lib is rather old and is mainly on what I would call "life support" and I do not plan to make a new major release - which would be required when breaking BC with - granted - seriously outdated PHP versions.

Other than that: The attributes added by @jrfnl fix the PHP 8.1 deprecation warnings. That won't make a promise it will work with PHP 8.2 or later but that's a different story. But by then we'd probably archived this project...

Sorry.