added websocket proxying support

[tverdohleb]

@Valian do you have any thoughts about this PR?

[Valian]

@tverdohleb First, thanks for this PR!

I would change two things here:

1. You are always adding Upgrade header. It should be done only for ws requests, like in the following snippet:

   http {
   map $http_upgrade $connection_upgrade {
       default upgrade;
       '' close;
   }
   
   upstream websocket {
       server 192.168.100.10:8010;
   }
   
   server {
       listen 8020;
       location / {
           proxy_pass http://websocket;
           proxy_http_version 1.1;
           proxy_set_header Upgrade $http_upgrade;
           proxy_set_header Connection $connection_upgrade;
       }
   }
   }

   Also, I believe proxy_http_version 1.1; directive is needed, as I have plans to add http 2.0 support

2. Could you also add a short note to README that this repository support websockets?

Sorry for a late reply, I have problems with GH notifications.

[srghma]

any update?

[Valian]

Replaced and implemented by #22