Don't return http 200 for ConnectHijack actions

Sending HTTP 200 back to the client connection before invoking the todo.Hijack() method for a ConnectHijack action makes it impossible to cascade the http 502 back to the client in case we wanted to abort prematurely (e.g.the target address is unavailable)

[RFC 2817](https://tools.ietf.org/html/rfc2817#section-5.3) States: 

```
5.3 Establishing a Tunnel with CONNECT

   Any successful (2xx) response to a CONNECT request indicates that the
   proxy has established a connection to the requested host and port,
   and has switched to tunneling the current connection to that server
   connection.
```

It should be therefore up to the Hijack() method implementer to send the http 200 upon confirming that we can establish a tunnel.

https.go

@@ -36,6 +36,10 @@ var (
 	httpsRegexp     = regexp.MustCompile(`^https:\/\/`)
 )
 
+// ConnectAction enables the caller to override the standard connect flow.
+// When Action is ConnectHijack, it is up to the implementer to send the 
+// HTTP 200, or any other valid http response back to the client from within the 
+// Hijack func
 type ConnectAction struct {
 	Action    ConnectActionLiteral
 	Hijack    func(req *http.Request, client net.Conn, ctx *ProxyCtx)
@@ -129,8 +133,6 @@ func (proxy *ProxyHttpServer) handleHttps(w http.ResponseWriter, r *http.Request
 		}
 
 	case ConnectHijack:
-		ctx.Logf("Hijacking CONNECT to %s", host)
-		proxyClient.Write([]byte("HTTP/1.0 200 OK\r\n\r\n"))
 		todo.Hijack(r, proxyClient, ctx)
 	case ConnectHTTPMitm:
 		proxyClient.Write([]byte("HTTP/1.0 200 OK\r\n\r\n"))