feat: filter out countries without public holidays

Fairly minor update, no code change, just added a new test to cover the
flag that was recently added to the API and expanded the documentation
to also include it.

README.md

@@ -67,6 +67,14 @@ try {
 $holiday_api->countries();
 ```
 
+#### Fetch only countries with public holidays
+
+```php
+$holiday_api->countries([
+  'public' => true,
+]);
+```
+
 #### Fetch a supported country by code
 
 ```php

composer.json

@@ -1,7 +1,7 @@
 {
   "name": "holidayapi/holidayapi-php",
   "description": "Official PHP library for Holiday API",
-  "version": "2.2.0",
+  "version": "2.2.1",
   "type": "library",
   "keywords": [
     "calendar",

tests/ClientTest.php

@@ -165,6 +165,40 @@ class ClientTest extends \PHPUnit_Framework_TestCase
         ), $client->countries(array('country' => 'ST')));
     }
 
+    public function testReturnCountryWithPublic()
+    {
+        $url = self::BASE_URL . 'countries?key=' . self::KEY . '&public=1';
+
+        $request = new Request(array(
+            'execute' => array(
+                $url => function ()
+                {
+                    return json_encode(array(
+                        'status' => 200,
+                        'countries' => array(
+                            array(
+                                'code' => 'ST',
+                                'name' => 'Sao Tome and Principle',
+                            ),
+                        ),
+                    ));
+                },
+            ),
+        ));
+
+        $client = new Client(array('key' => self::KEY, 'handler' => $request));
+
+        $this->assertEquals(array(
+            'status' => 200,
+            'countries' => array(
+                array(
+                    'code' => 'ST',
+                    'name' => 'Sao Tome and Principle',
+                ),
+            ),
+        ), $client->countries(array('public' => true)));
+    }
+
     public function testCountriesRaise4xxErrors()
     {
         $url = self::BASE_URL . 'countries?key=' . self::KEY;