added a simple way to override the Twig environment instance
added a simple way to override the Twig environment instance

silexphp/Silex,romainneutron/Silex,romainneutron/Silex,fabpot/Silex,akucherevskiy/developex_test,akucherevskiy/developex_test,romainneutron/Silex,mTorres/Silex,akucherevskiy/developex_test,fabpot/Silex,mTorres/Silex,gencer/Silex