A new way to set up transparent proxying

[yrutschle]

@ftasnetamot came up with a new way to set up transparent proxying, which is much easier and clearer than the previous one.

Try it out, here are all his explanations:
https://github.com/yrutschle/sslh/blob/master/doc/simple_transparent_proxy.md
https://github.com/yrutschle/sslh/blob/master/doc/scenarios-for-simple-transparent-proxy.md