auto-tunnel with env vars

[stevenvachon]

const url = "http://domain/";

https.request({
  url: url,
  agent: tunnel.auto(url)
});

I've written a separate, currently unpublished package here: https://github.com/stevenvachon/auto-tunnel

Is this something you'd be interested in accepting as a PR?

[stevenvachon]

@mikeal ^