Mock network requests

[pathawks]

Some sites make extensive use of network APIs while building.

It would be nice to totally eliminate this as a build time variable. This would require a Ruby wrapper around Jekyll that would mock all network requests instead of sending them across the wire.

The most obvious one would be the GitHub Pages API, which could just return a static object with dummy site info. I think there are some other APIs too that would need to be recreated with some static data.