Django-sudo

- Added `sudo.views.SudoView` class based view. This is now more extensible and
should be preferred over the older `sudo.views.sudo` view function.
- Removed `SUDO_FORM` setting. It's now suggested to subclass `sudo.views.SudoView`
and override `form_class`.
- Added `SUDO_URL` setting to set the url for the sudo page.

- Verified compatibility with python 3.5 and pypy3
- Verified compatibility with Django 1.8
- Dropped support for python 3.2
- Better support for custom User models. See 4
- Added a `SudoMixin` for use with class based views. 5