subnet implementation (filter, parsing tags) #2560

…DR with correct recognition of IP-family), provides new replacement tags for failregex to match subnets in form of IP-addresses with CIDR mask (fail2bangh-2559): - `<CIDR>` - helper regex to match CIDR (simple integer form of net-mask); - `<SUBNET>` - regex to match sub-net adresses (in form of IP/CIDR, also single IP is matched, so part /CIDR is optional);