Feature request: parent proxy and portable mode

[Null-Kelvin]

Thanks for the great software!
Privaxy is almost perfect, but it missed two things:
Firstly - it can't work in a proxy chain, so I need to choose between Privaxy and other proxies. For proxy chaining there is should be an option for disable MitM-mode - it's not always necessary. Theoretically, proxy chaining can help with hiding Privaxy behind reverse-proxy and transparent proxying.
Secondly - config path shouldn't be hard-coded.