define host / scheme / relative path for agnostic paths

[klibansky]

I would like to be able to control the cache output path to //path/to/file.js. It would be nice to also control the host. For example, on my dev machine I have a host name set like: domain.dev as http and https. It would be nice to have the output path be or // or http or https depending on how I access the website. Also, on other devices in my network I use xip.io to resolve local hostnames but that changes the hostname to: domain.ext.192.168.0.2.xip.io. So on those devices the js and css is not loaded because it can't access the paths.