Fix and improve reflection

- use "p" for path (security check for nul byte)
- fix number of args for some methods
- add type hinting
- throw standard exception (simplify)
- fix test suite for PHP 7.0 to 8.0

tests/cnn_face_detection_ctor_error.phpt

@@ -6,10 +6,10 @@ Testing CnnFaceDetection constructor without arguments
 <?php
 try {
 	new CnnFaceDetection();
-} catch (Exception $e) {
+} catch (Error $e) {
 	var_dump($e->getMessage());
 }
 ?>
 --EXPECTF--
-Warning: CnnFaceDetection::__construct() expects exactly 1 parameter, 0 given in %s on line 3
-string(41) "Unable to parse face_detection_model_path"
+string(68) "CnnFaceDetection::__construct() expects exactly 1 parameter, 0 given"
+