Add Socks5 support

[goodloop]

[jhillyerd]

It's not currently supported. It probably wouldn't take much to add, but I (thankfully) no longer work at a company that requires a proxy.

I've never used a socks proxy, if it's something that can be added using the same hostname as all the HTTP/FTP proxies, and a standardized port number - then I would accept a pull request for it. I feel like we may need to have a flag though, as I think proxies that don't support socks may break a lot of apps otherwise.

You'd want to look at:

https://github.com/oh-my-fish/plugin-proxy/blob/master/functions/proxy.fish https://github.com/oh-my-fish/plugin-proxy/blob/master/functions/__proxy.set.fish