Replace overture with kotlin?

[Mygod]

Yeah, with this we will no longer need overture methinks. So check it out IDK cuz I am not gonna touch this for a while. @madeye

Nothing works yet (well actually receiving DNS and local resolver work) and somebody just needs to debug this I guess.

See also PR for dnsproxyd: shadowsocks#2092

[With this PR, we] can also respect local DNS settings (fix shadowsocks#2016), and therefore including possibly support private DNS on Android 9+ (see also shadowsocks#2015).

P.S. It seems like private DNS is not working on my side with Wi-Fi + VPN but works fine with mobile data + VPN. Can anyone also confirm this?

[Mygod]

@madeye Meanwhile, we can choose to do either: (if you think dnsproxyd is good enough, I think it looks to me for now)

• Merge Mygod:dnsproxyd -> shadowsocks:master and move this PR to shadowsocks;
• Push Mygod:dnsproxyd -> shadowsocks:dnsproxyd and move this PR to shadowsocks.

[Mygod]

Also I believe Kotlin coroutines have comparable performance with goroutines [1] [2] [3], but obviously that needs fine tuning. The current code probably runs a little slow but again code in overture was not written with great care either.

[madeye]

Yeah, let's move this PR to shadowsocks first.