Add experimental KCPTUN support.
KCPTUN should run as a plugin server of shadowsocks server.
Example:
Run a KCPTUN on your server, listening on port 53, redirecting to shadowsocks port 8388:
sudo kcptun -l :53 -t 127.0.0.1:8388 --crypt none --mtu 1024 --sndwnd 1024 --rcvwnd 1024 --mode fast --nocomp
Then the parameters for the client is:
--crypt none --mtu 1024 --sndwnd 1024 --rcvwnd 1024 --mode fast --nocomp