* Got rid of ConfigError from exceptions.py.
* Try to load config ourselves if it isn't already, via the new _load_config()
method of Site. It uses getpass if passwords are encrypted, as done by
earwigbot.py.
* Cleaned up UserNotFoundError in user.py and exceptions.py.
User: added .get_rights() (working) and .exists() (skeleton).
Page: added .exists() (skeleton); store text as ._content; get() has a force_reload argument.
Category: fixed missing self in .get_members().
Site: self.__api -> self._api; self.__sql -> self._sql