Support HTTP and SOCKS5 proxy on the same port using proxy mux

[bobpaul]

The tailscale project has a neat feature where their proxy accepts connections from either HTTP or SOCKS5 proxy clients. The relevant upstream package is proxymux,

Here's an example project using proxy mux.

Tailscale's documentation explains why this feature is convenient, but basically it allows one to set ALL_PROXY, HTTP_PROXY, http_proxy environment variables and applications will be able to use the proxy regardless of whether they implemented support for socks, http proxy, or both.