* Add extension extb_guest
This module provides an extban type that acts as a normal ban but
only matches unidentified users.
* Document extban g in help/opers/extban
* extensions/extb_guest: support CIDR masks in $g extbans
This allows a channel operator to set a channel ban such as
"$g:*!*@192.0.2.0/24#*web.libera.chat*" and have it function
as intended.
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Co-authored-by: Aaron Jones <me@aaronmdjones.net>