Async* trait implementations for StdinLock, StdoutLock, StderrLock #346
Description
As far as I can tell, AsyncWrite is not implemented for StdoutLock and StderrLock, and AsyncRead is not implemented for StdinLock. I'm not sure if it makes sense to implement them for these, but I thought I might as well make the issue in case it's an oversight since I couldn't find an existing one.