dastan

GoDoc on net.Conn says `Multiple goroutines may invoke methods on a Conn simultaneously.` [shadowsocks/conn](https://github.com/shadowsocks/shadowsocks-go/blob/master/shadowsocks/conn.go#L15) doesn't follow the thread-safe assumption, this may break some code in future use.

In section 3.1.3 and 4.1.2 HMAC examples, I believe the sentence `"For an HMAC-based signature without a list of headers specified"` should be `"For an HMAC-based signature with a list...