Allow for custom subdomains

[xori]

site-1.127.0.0.1.backname.io doesn't seem to resolve to 127.0.0.1 like I'd expect.

This would be useful for virtual host config setups, so devs (and myself) wouldn't have to modify our host files when we want to develop multiple sites at the same time.

• site-1.0--1.backname.io
• site-2.0--1.backname.io

All resolving to ::1 would also be super handy (and short!) url options.

[Twixes]

Good point, that's a use case I missed. Will add support for this.

[Twixes]

This is not yet advertised on the website, but it's supported now.