Fix/performance issues

Allows ```socket.io-stream``` to support ```push``` streams instead of ```pull``` only.

Pull streams force the client to send the server a read command for every single write command which causes a laggy experience when ```socket.io-stream``` is used interactively for example.

Push streams basically allows the ```server/client``` to push data to the other side without it having to send a ```read command```.

:warning: This currently breaks some of the acceptance tests (the file streaming ones), all other tests are good.