Upstream iOS and macOS support from berty/go-libtor

Thanks for working on this library, it's a really neat approach!

I have seen that some people have added support for iOS and macOS and I am wondering if you could consider upstreaming the changes so that we can consolidate efforts in a single repo: https://github.com/berty/go-libtor/issues/6.

I would be happy to help out in any way I can to aid in the process.