php can find it when `sparkline/Sparkline.php` is required.
* The GD PHP module used by the Sparkline library.
* A "php" program in the path, that can run standalone php programs.
php can find it when `sparkline/Sparkline.php` is required.
* The GD PHP module used by the Sparkline library.
* A "php" program in the path, that can run standalone php programs.