final touches
Replace ... with etc
Fix typos in cookbook/testing/database
Add versionadded tag to security config reference, reference cookbok entry in book
remove versionadded from book and fix words
change wording in versionadded example to be consistent with what we use today
[Reference][Form Types] Add missing "format" option to "datetime" field
enclose YAML string with double quotes to fix syntax highlighting
[WIP][Valiadtor] - EmailConstraint reference
Use of Sphinx markup
Version added and clarifications
Link moved and heading updated
fixed typo
Fixed `versionadded` inconsistencies
Fixed `versionadded` inconsistencies
Typo and link label
Fix according to PR comments
Lowercase and link label
Changed extends to implements
Update custom_password_authenticator.rst

Correct me if I am wrong... but because we are passing here ```username``` as first argument to ```UsernamePasswordToken```, when one would like to use method ```getUser()```: 
```
...
if (!$this->container->has('security.context')) {
            throw new \LogicException('The SecurityBundle is not registered in your application.');
        }

        if (null === $token = $this->container->get('security.context')->getToken()) {
            return null;
        }

        if (!is_object($user = $token->getUser())) {
            return null;
        }

        return $user;
...
```
from base ```Controller```, it will fail, to get actually logged user and return null.