Add native vector_lenght() function which calculates the euclidean distance 80%

faster. See https://github.com/matiasdelellis/pdlib/pull/2.

Increase the version to 1.0.2 since this is a required function for our
application and we must control it.

Add more compilation info in php-info(), and print a final message with the
build options when configure.

Fix that when dlib is not installed, the configuration returns that it cannot
find pkgconfig. See https://github.com/matiasdelellis/facerecognition/issues/261

Also implement the test on travis. See for example:
(https://travis-ci.com/github/matiasdelellis/pdlib/builds/161854044)

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"