Symfony3 support

Merge pull request #35 from christoph-hautzinger/patch-1

made bundle ready for symfony3

use PSR-4 autoloading

#29

Switch the Twig integration to use non-deprecated APIs

#30

Symfony 2.7 compatibility

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

no need to bootstrap HTML Purifier when using composer autoloader.

v0.1.0

Merge pull request #18 from shieldo/use_composer_for_tests

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