Feature request: --exclude-private-hosts

[tamalsaha]

Thanks for this tool. We are using this tool with Github actions to make sure our docs don't have invalid urls.

One of the common pattern for us is that our docs have localhost addresses and domains with non-public TLD. Currently I am using --exclude pattern to skip those. But this making the --exclude pattern very long and hard to read. I think it will be very handy to add a --exclude-private-hosts to avoid private domains and private ips.

If you are open to this, I can send a pr.

[tamalsaha]

I have opened a pr #29