* Exceptions: New PermissionsError; reworded docstring of SiteAPIError.
* Site: __init__() accepts an optional cookiejar parameter, otherwise we
  use CookieJar(). Added five new cookie/username-related methods. Only
  login from __init__() if we are missing valid login cookies and a user/
  pass was provided. _login() and _logout() both try to save cookies via
  _save_cookiejar(). _load_attributes() automatically refreshes all
  attributes other than namespaces if at least one is missing, instead of
  only the missing ones. api_query() raises SiteAPIError if either
  self._base_url or self._script_path is missing. Removed some pointless
  methods and renamed one; added domain().
* Functions: _get_site_object_from_dict() is cleaner, adds our cookiejar
  to Site instances using _get_cookiejar() to load a LWPCookieJar() object
  from the ".cookies" file in our project root. The same cookiejar is
  returned for every site, enabling crosswiki login, via a global variable.
* User: Renamed some methods.
* .gitignore: Added .cookies file.