Wireguard support for Mullvad and Windscribe (#565)

- `internal/wireguard` client package with unit tests
- Implementation works with kernel space or user space if unavailable
- `WIREGUARD_PRIVATE_KEY`
- `WIREGUARD_ADDRESS`
- `WIREGUARD_PRESHARED_KEY`
- `WIREGUARD_PORT`
- `internal/netlink` package used by `internal/wireguard`

docker-compose.yml

@@ -15,10 +15,11 @@ services:
     volumes:
       - /yourpath:/gluetun
     environment:
-      # More variables are available, see the readme table
+      # More variables are available, see the Wiki table
       - OPENVPN_USER=
       - OPENVPN_PASSWORD=
       - VPNSP=private internet access
+      - VPN_TYPE=openvpn
       # Timezone for accurate logs times
       - TZ=
     restart: always