Django-registration-email

- made username generation more robust to avoid name clashes

- Added method `generate_username` in `forms.py` so you can re-use it in your
own apps.

- Added new settings: REGISTRATION_EMAIL_REGISTER_SUCCESS_URL and
REGISTRATION_EMAIL_ACTIVATE_SUCCESS_URL. This allows to override the standard
redirect without overriding the urls.py.

- Added URLs for the simple backend of django-registration.

- Initial commit