Add binary switch support to socketio engine

[jfkz]

There is a feature in socket.io that can transfer binary data between server and client sockets:
https://socket.io/docs/server-api/#Flag-%E2%80%98binary%E2%80%99-1

I write simple solution to support this but cant create tests for it (request help).

Please, review and comment if there is something wrong.

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