HAProxy implementation in TCPProxy option.

Since SOCKS5 takes 2 round trips, SOCKS4 doesn't support IPv6 and the proxy has to support DNS resolving in HTTP CONNECT, I would like to implement the proxy protocol of HAProxy to support IPv6 and the proxy doesn't have to resolve domain names by itself.

According to the mail thread, https://lists.torproject.org/pipermail/tor-dev/2019-August/013968.html, people suggested to create a new torrc option called TCPProxy and have a protocol as a parameter.