Fix #347: Add basic support for requests using relative paths

examples/get_relative.php

@@ -0,0 +1,20 @@
+<?php
+require __DIR__ . '/../vendor/autoload.php';
+
+use \Curl\Curl;
+
+$curl = new Curl('https://www.example.com/api/');
+
+// https://www.example.com/api/test?key=value
+$response = $curl->get('test', array(
+    'key' => 'value',
+));
+assert('https://www.example.com/api/test?key=value' === $curl->url);
+assert($curl->url === $curl->effectiveUrl);
+
+// https://www.example.com/root?key=value
+$response = $curl->get('/root', array(
+    'key' => 'value',
+));
+assert('https://www.example.com/root?key=value' === $curl->url);
+assert($curl->url === $curl->effectiveUrl);