code: static public function addParams($url, $params)
      {
          $query = parse_url($url, PHP_URL_QUERY);
          $separator = (Text::isEmpty($query)? "?" : "&");
          return Text::concat($separator, $url, http_build_query($params));
      }
docs: Appends parameters to a given url.
  
  For example:
  ```php
  echo Http::addParams("http://www.mysite.php", array("username" => "John", "id" => 101));
  ```
  
  @param string $url    URL
  @param array  $params Associative array of parameters
  
  @return strings.