consider switching to openvpn3

this has been in talks for a while, but recently I found https://github.com/mysteriumnetwork/go-openvpn which seems mature. I wonder if a bitmask golang library that wraps c++ could be usable from android/iOS

probably a minimal prototype can be done to play with. what do you think @cyberta?

edit: after opening this issue I saw this

./gomobile_ios.sh -o build/Openvpn3.framework

so yes, way to go.