Reduce memory footprint from kcp-go.
(https://github.com/xtaci/kcp-go/blob/master/kcp.go#L204)
(STRONGLY RECOMMENDED FOR UPGRADING)
$ go version
go version go1.7.3 darwin/amd64
xtaci/smux@9d1cf79
xtaci/kcp-go@2220e8c
bb9574e
MD5 (kcptun-linux-amd64-20161028.tar.gz) = 698cb00a420b98c8c7a7d096db0b2720
MD5 (kcptun-linux-386-20161028.tar.gz) = ab76de6934b816a77ce5119705198924
MD5 (kcptun-darwin-amd64-20161028.tar.gz) = 2ed9c4e6d9da51eee9d55fab962ffd8d
MD5 (kcptun-darwin-386-20161028.tar.gz) = 4ad1dd2aca302f4683356a1c3d0a32bb
MD5 (kcptun-windows-amd64-20161028.tar.gz) = 06ff5cc02e173a4f9b2aa4bfc4c949e7
MD5 (kcptun-windows-386-20161028.tar.gz) = 4aabae9d1831fc4a4a636e4af053a051
MD5 (kcptun-freebsd-amd64-20161028.tar.gz) = a7c6f4946f870e200efa5ebdc24defeb
MD5 (kcptun-freebsd-386-20161028.tar.gz) = 89bde3529be712253d7c352db56eedc1
MD5 (kcptun-linux-arm-20161028.tar.gz) = 05449422a35a0e5845e172b256299af9