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Hello,

Thanks for the work to make dockerpty work without the tty :)

I noticed however, that it will quit if you enter anything on stdin.

So I've got a change here to only hijack the tty for the streams that are set to be attached in the config for the container.
Personally I think it's not needed. The chance of the call `set_blocking()` failing is extremely slim (at least as used in this codebase). I tend to cut out code like this and just let it crash loudly (as it should if the assignment fails). I think I got that idea drummed into me from learning Erlang.