Basic LDAP support

Hi,

I've been working on implementing LDAP support to ZfcUser (first tried as another ZF2 module, but I'm too new to Zf2)

This changes that I've made are working; again I'm new to ZF2 and to ZfcUser, so please feel free to request any changes or things that you would like to work different, also take note on the following to be able to use LDAP auth:
- You must create a zfcuser.ldap.local.php file in your config/autoload dir
- You must also create a zfcuser.global.php file in your config/autolad dir with this value:
        'enabled_auth_methods' => array( 'ldap' )
- Take note that this config change will automatically modify the value for:
        auth_identity_fields (always set to array( 'username' ))
        enable_registration (always set to false)

Hope this helps anyone :-)

Greetings!
Gonzalo G.