check on symfony 2.1

[jaytaph]

This needs to be checked if it all still works on symfony 2.1. If a 2.0 and 2.1 version are not compatible, we must create two separate branches/tags probably.

[basdenooijer]

The two are not compatible, though the required changes are not too complicated. The master branch is now for 2.1 development, a separate 2.0 branch was created to keep support for Symfony 2.0.

The code in de master branch is not yet updated for 2.1, but PR #5 should fix that.