Banned users can be configured in the setup file via the `banned_users`
setting. This is a list of user names, or [[PageSpecs|ikiwiki/PageSpec]]
to ban. Using a PageSpec is useful to block an IP address.

For example:

	banned_users => ['evilspammer', 'ip(192.168.1.1)'],

If a banned user attempts to use the ikiwiki CGI, they will receive a 403
Forbidden webpage indicating they are banned.
