Add PHP templating engine support

This PR adds support for the PHP templating engine & so, fix #29. 

It uses #32 as base but I propose it in a new PR as it will be hard for @geoffrey-brier to rebase his work on top of the last updates...

Before merging, I would like to fix the "FIX ME" part of this PR (for Twig too) & add some tests about templates (generate each of them & check if the output is right).