There are multiple ways to include the PHP parser into your project:
Run the following command inside your project:
php composer.phar require nikic/php-parser
If you haven't installed Composer yet, you can do so using:
curl -s http://getcomposer.org/installer | php
Run the following command to install the parser into the vendor/PHP-Parser
folder:
git submodule add git://github.com/nikic/PHP-Parser.git vendor/PHP-Parser
Download the latest version from the download page, unpack it and move the files somewhere into your project.