PHP_CodeSniffer version 2

makes this Symfony2 coding standard compatible with squidlab's PHP_CodeSniffer version 2

###### note:
the approach for dealing with the ``{@inheritdoc}`` comments is similar to the original approach in this repo. according to this discussion: https://github.com/squizlabs/PHP_CodeSniffer/pull/214 there might be a better solution for these kind of comments in a future version of PHP_CodeSniffer