update to 2.6.2
    raise dependency on PHP 7.1
    add dependency on doctrine/annotations
    raise dependency on doctrine/cache 1.6
    raise dependency on doctrine/collections 1.4
    raise dependency on doctrine/common 2.7.1
    raise dependency on doctrine/dbal 2.6
    raise dependency on doctrine/instantiator 1.1
    switch to symfony 3 and 4
    switch to phpunit6