Feature request: environment vars

Hi @extremecoders-re (and @David-Lor) ,

This fork supports environment variables: https://github.com/David-Lor/socks-proxy-balancer

It also has implemented support for config files. And the code is encapsulated inside one file: https://github.com/David-Lor/socks-proxy-balancer/blob/develop/src/settings.go

I suggest to include this implementation in the main project.
You agree?
