Added Doctrine Entity Roles

This is my first ever pull request so I hope I've done this right!

Description
----------------
I recently started using BjyAuthorize with Doctrine and didn't like the fact that I had to import the schema.sql and then write a layer above that to make it possible to manage the permissions so I decided to make a Roles entity which linked to a User entity. After a bit of thought I thought others might like this too so I wrote it into the module.

Usage
---------
The usage is very simple:

Firstly you need to be using ZfcUserDoctrineORM

Next in your ZfcUser configuration specify `BjyAuthorize\Entity\User` for the **user_entity_class** setting

Then in you bjyauthorize settings include the following 2 options:

    identity_provider'     => 'BjyAuthorize\Provider\Identity\ZfcUserDoctrineEntity',

    'role_providers'        => array(
            'BjyAuthorize\Provider\Role\DoctrineEntity' => array(
            //    'role_entity_class' => 'BjyAuthorize\Entity\Role',
            ),
),