Add support for setting some manual records

Allows user to specify static records by using `--record <name>:<ip>`
ie, `docker run docker-dns --domain test --record service:127.0.0.1`
which lets you resolve service.test to 127.0.0.1

**Note:** the ip-address parsing is optimistic at best and will only work for IPv4. The result being that you can specify out of range ip addresses like `127.0.0.299`.