PHP Sitemap abstraction library

---

1. Add urls one-by-one

   $urlset = new Urlset($links);
   
   foreach(range('a', 'z') as $letter) {
            $url = new Url(
                'https://vocabula.ry/'.$letter,
                new \DateTime('2017-01-01 00:00:01'),
                Url::CHANGEFREQ_MONTHLY,
                0.8
            );
            
            $url->addImage(new Image('https://test.com/image/'.$i));
            $url->addVideo(new Video('https://test.com/video/'.$i, 'Title '.$i, 'Description '.$i));
            $url->addNews(new News('Awesome news '.$i, '2018-01-01', 'Awesome news name '.$i, 'ru-RU'));
            
            $urlset->addUrl($url);
        }
    
   
   $sitemap = new Sitemap($urlset);
   
   $sitemap->toXmlString();
   $sitemap->toTxtString();
   $sitemap->write(__DIR__ . '/sitemap.xml');
   $sitemap->write(__DIR__ . '/sitemap.txt', Sitemap::FORMAT_TXT);

2. Using links generator

   $links = function() {
        foreach(range('a', 'z') as $letter) {
            $url = new Url(
                'https://vocabula.ry/'.$letter,
                new \DateTime('2017-01-01 00:00:01'),
                Url::CHANGEFREQ_MONTHLY,
                0.8
            );
            
            $url->addImage(new Image('https://test.com/image/'.$i));
            $url->addVideo(new Video('https://test.com/video/'.$i, 'Title '.$i, 'Description '.$i));
            $url->addNews(new News('Awesome news '.$i, '2018-01-01', 'Awesome news name '.$i, 'ru-RU'));
            
            yield $url;
        }
   }
    
   $urlset = new Urlset($links);
   $sitemap = new Sitemap($urlset);
   
   $sitemap->toXmlString();
   $sitemap->toTxtString();
   $sitemap->write(__DIR__ . '/sitemap.xml');
   $sitemap->write(__DIR__ . '/sitemap.txt', Sitemap::FORMAT_TXT);

3. Sitemap index

   $index = new Sitemapindex();
   $sitemap = new Sitemap($index);
   
   foreach (range(1, 2) as $i) {
       $sitemap = new SitemapindexSitemap(
           'http://test.com/'.$i,
          '-1 year'
       );
       $index->addSitemap($sitemap);
   }
   
   $content = $sitemap->toXmlString();