Option to set the DC2Type- Comment on custom types

[tommyseus]

Added a a new option to mark types as commented.
It will create the comment (DC2Type:point) on custom types.

Inspired by \Doctrine\Bundle\DoctrineBundle\ConnectionFactory

Config example:

return array(
    'doctrine' => array(
        'connection' => array(
            'orm_default' => array(
                'doctrineTypeMappings' => array(
                    'point' => 'string',
                ),
                'doctrineCommentedTypes' => array(
                    'point'
                ),
            ),
        ),
        'configuration' => array(
            'orm_default' => array(
                'types' => array(
                    'point' => '\MyNamespace\PointType',
                ),
            ),
        ),
    ),
);

[Ocramius]

@gianarb looks good to me (except for missing tests)

[gianarb]

Replace with #437