Implement dlib_vector_length to calculate the euclidean distance of the vectors

It not use the 'length' native versions of dlib, due I have to convert the
array to the vector, which will take the same time, and then I will use the
native method.

tests/version.phpt

@@ -0,0 +1,10 @@
+--TEST--
+Just test php extension version
+--SKIPIF--
+<?php if (!extension_loaded("pdlib")) print "skip"; ?>
+--FILE--
+<?php
+var_dump(phpversion('pdlib'));
+?>
+--EXPECT--
+string(5) "1.0.2"