support convert method connect to websocket
support convert method connect to websocket

* browser access https through forward proxy1
* proxy1 will accept connect request
* proxy1 will proxy to proxy2 by upgrade/websocket
 - proxy1 will set headers[x-method-ori] to the original request method
 - proxy2 may be deployed in cloud behind a reverse proxy
 - the reverse proxy in cloud may only allow normal and websocket request
 - and forbid connect request
 - proxy2 is located in a free net env, it's not under network restriction
* proxy2 will connect to the target site, its https
* proxy2 will response with 101 switch protocol
* proxy2 will response with Connection Established next
* when proxy1 accept 101, it can not auto response with 101, but ignore it

kaven276/node-http-proxy