Сompatibility with Symfony 2.1.* (twig 1.12.*)

Please, upgrade the bundle to be compatible with Symfony 2.1.*.

Need to apply the next changes:  
- when creating twig extention use Twig_SimpleFunction to add functions (@see  
<https://github.com/fabpot/Twig/blob/master/doc/deprecated.rst#functions>). 

@use docs http://twig.sensiolabs.org/doc/advanced.html#id2 to properly define the extension functions.


*Many thanks for considering my request.*