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)

php_pdlib.h

@@ -31,7 +31,8 @@ extern "C" {
 extern zend_module_entry pdlib_module_entry;
 #define phpext_pdlib_ptr &pdlib_module_entry
 
-#define PHP_PDLIB_VERSION "1.0.1" /* Replace with version number for your extension */
+#define PHP_PDLIB_VERSION "1.0.2"
+#define PHP_PDLIB_NAME     "pdlib"
 
 #ifdef PHP_WIN32
 #	define PHP_PDLIB_API __declspec(dllexport)