restrict: add CIDR notation.

so instead of this:
restrict 10.169.0.0 mask 255.0.0.0
restrict 2001:470:e34c:2:: mask ffff:ffff:ffff:ffff:ff00::

You can do this:
restrict 10.169.0.0/8
restrict 2001:470:e34c:2::/72

Documentation update to follow.