If the ResponseWriter implements any of the following methods,
the ResponseController will call them as appropriate:
Flush()
FlushError() error // alternative Flush returning an error
Hijack() (net.Conn, *bufio.ReadWriter, error)
SetReadDeadline(deadline time.Time) error
SetWriteDeadline(deadline time.Time) error
EnableFullDuplex() error
If the ResponseWriter doesn't implement the methods,
the ResponseController will call Unwrap() method until it
finds a ResponseWriter in the chain
This commit implements Unwrap() method to simply return the
wrapped ResponseWriter
Signed-off-by: Igor Drozdov <ihardrozdov@gmail.com>