Optimizations on CPU Usage
- improve xor.go performance by re-organizing code layout.
- dramatically reduce zero-ing operations in FEC.
$ go version
go version go1.4.2 linux/amd64
xtaci/smux@ee8b5b5
xtaci/kcp-go@7112c1c
xtaci/kcptun@4ccc922
$ go version
go version go1.4.2 linux/amd64
xtaci/smux@ee8b5b5
xtaci/kcp-go@7112c1c
xtaci/kcptun@4ccc922