Fix multiple websocket connection issues.

[bridadan]

I was testing the ws_server and ws_client examples and I hit multiple issues. I've attempted to fix them with these changes, but I'm not 100% sure if this is the "right" way. Thanks for the great library and for considering this change!

• The websocket client sends two Connection headers:

  HTTP/1.1 GET /
  Host: 127.0.0.1
  Origin: foo.com
  Content-Length: 0
  Connection: Upgrade
  Upgrade: websocket
  Sec-WebSocket-Version: 13
  Sec-WebSocket-Key: h57ZiKx+KAwmKbB+mxR8Ag==
  Connection: Keep-Alive

  The last "Connection: Keep-Alive" is added because the ConnectionType enum does not have an "Upgrade" variant. Adding the variant prevents this issue.

• If the websocket client does not receive a "Content-Length: 0" header in the server's response, an error is returned stating "Unknown body type in a response with a Keep-Alive connection. This is not allowed." This occurs with the example client using the "websockets.chilkat.io/" service. This is corrected by assuming a "BodyType::ContentLen(0)" for the response when no other BodyType is provided and the "Connection: Upgrade" header is present.

[ivmarkov]

Actually, your fix looks exactly what we should do!
(And yes - sorry for the headache - I must admit I forgot to test the ws_client/server code with the edge-http changes that introduced the notion of ConnectionType!)

If you fix the formatting issues and the CI passes, I'll merge asap.

[bridadan]

Thanks!

[ivmarkov]

Ill release a new edge-http 5.x patch as well these days. In theory, it should be a breaking release, because we added a new member to a #[non_exhaustive] enum but maybe we can squint a little for that...