Add a command-line option to allow destinations by domain name

[SpecLad]

Currently it seems like the only options to allow internal destinations are by IP address range --allow-range or by IP address (--allow-address). It would be useful if I could allow specific domain names as well (e.g. --allow-domain=my-server, or --allow-domain=*.my-domain.com).

It seems that this is already possible with an ACL file, but it would be nice to be able to set this via command-line options too.