Added PHP Pandas online book

Added Dayle Rees's PHP Pandas book to the PHP list.

free-programming-books.md

@@ -1631,6 +1631,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [PHP 5 Power Programming](http://www.informit.com/content/images/013147149X/downloads/013147149X_book.pdf) (PDF)
 * [PHP Best Practices](https://phpbestpractices.org)
 * [PHP Internals Book](http://www.phpinternalsbook.com)
+* [PHP Pandas](http://daylerees.com/php-pandas/) - Dayle Rees
 * [PHP Programming](https://en.wikibooks.org/wiki/PHP_Programming)
 * [PHP Security Guide](http://phpsec.org/projects/guide/)
 * [PHP: The Right Way](http://www.phptherightway.com)