Provide IPAddress type

If you want to work with a complete socket address type including port, we have a helper in SocketAddress. However, the moment you want to talk only about an IP address we force you to hold an in_addr or in_addr6 structure: hardly the friendliest versions of these data types.

We should provide a helpful wrapper IPAddress type that can be converted into those types as needed. This would be a much friendlier way to work with IP addresses. This is a good issue for those who are familiar with either IP addresses or Swift.