implement candidate compromise proposal for websockets

1. Text and binary frames are accepted
2. Text frames are sent by default
3. Binary frames are sent to clients who negotiate `binary.ircv3.net`
4. Non-UTF8 data is not accepted (enabling websockets still enables UTFONLY)

irc/client.go

@@ -691,7 +691,7 @@ func (client *Client) run(session *Session) {
 		} else if err != nil {
 			var quitMessage string
 			switch err {
-			case ircreader.ErrReadQ, errWSBinaryMessage:
+			case ircreader.ErrReadQ:
 				quitMessage = err.Error()
 			default:
 				quitMessage = "connection closed"