Add CIDR network notation for allow/deny

[systemofapwne]

It would be useful, if CIDR notation is supported for networkl/ip ranges.

In apache, a config like this is working:

    order deny,allow
    deny from all
    allow from 10.0.0.0/8

Here, it rejects my test ip 10.100.4.2 which clearly is covered by 10.0.0.0/8 . Further masking network bits up to 10.100.4.0/24 did not work either.
But adding the single ip 10.100.4.2 indeed worked. So I assume, CIDR notation is not implemented.

[systemofapwne]

Note: One might consider https://github.com/api7/lua-resty-ipmatcher for this and replace ip_matches_mask with it.