Fixes panic due to unimplemented method when the stdlib http server
calls this under certain conditions.
For our mitm implementation of net.Conn, an empty address string should be sufficient.
Timeouts should be handled by the http stack for the underlying tcp
connections so noops are appropriate for this virtual connection. No
need to panic.
Add http2 using the go-1.6 net/http built-in support.
net/http's http2 doesn't support hijacking, so instead of hijacking the
inital CONNECT tcp connection, tunnel proxied requests/responses over
the reader and writer streams of the CONNECT request.
