RFC 3892 Support

[wakamoleguy]

https://tools.ietf.org/html/rfc3892

I believe basic support for this can be achieved application-side, but @funkycode suggested that including default behavior may be nice. From an API perspective, I could see this as an option passed to the refer() method, as well as an optional argument to followRefer() for the referee to opt in or out when copying the headers over.

See the original pull request for some commentary and code:

#77

[egreenmachine]

Can you try out #459? I think that I have addressed this issue there.

• Due to the age of this issue, if we do not hear any feedback on this we will close it once we merge the pull request.