Merge pull request Exercise#30 from stof/patch-1

Switch the Twig integration to use non-deprecated APIs

Merge pull request Exercise#21 from caxy/feature/no-bootstrap

no need to bootstrap HTML Purifier when using composer autoloader.

Merge pull request Exercise#18 from shieldo/use_composer_for_tests

add symfony/twig to composer.json, and make test suite boot using composer autoload