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)

src/vector.cc

@@ -0,0 +1,43 @@
+
+#include "../php_pdlib.h"
+
+#include "vector.h"
+
+#include <cmath>
+#include <zend_exceptions.h>
+#include <iostream>
+
+using namespace std;
+
+PHP_FUNCTION(dlib_vector_length)
+{
+	zval *x_arg, *y_arg;
+
+	if (zend_parse_parameters_throw(ZEND_NUM_ARGS(), "aa", &x_arg, &y_arg) == FAILURE) {
+		return;
+	}
+
+	zval *elem_x, *elem_y;
+	double sum = 0.0;
+	unsigned int i, len;
+
+	len = zend_hash_num_elements(Z_ARRVAL_P(x_arg));
+
+	if (len != zend_hash_num_elements(Z_ARRVAL_P(y_arg))) {
+		zend_throw_exception_ex(
+			zend_ce_exception,
+			0,
+			"The arrays have different sizes");
+		return;
+	}
+
+	for (i = 0 ; i < len ; i++) {
+		elem_x = zend_hash_index_find(Z_ARRVAL_P(x_arg), i);
+		elem_y = zend_hash_index_find(Z_ARRVAL_P(y_arg), i);
+
+		sum += (Z_DVAL_P(elem_x) - Z_DVAL_P(elem_y))*(Z_DVAL_P(elem_x) - Z_DVAL_P(elem_y));
+	}
+
+	RETURN_DOUBLE(sqrt(sum));
+}
+

src/vector.h

@@ -0,0 +1,10 @@
+#ifndef PHP_DLIB_VECTOR_H
+#define PHP_DLIB_VECTOR_H
+
+ZEND_BEGIN_ARG_INFO_EX(dlib_vector_length_arginfo, 0, 0, 2)
+    ZEND_ARG_ARRAY_INFO(0, x_arg, 0)
+    ZEND_ARG_ARRAY_INFO(0, y_arg, 0)
+ZEND_END_ARG_INFO()
+PHP_FUNCTION(dlib_vector_length);
+
+#endif //PHP_DLIB_VECTOR_H