Why does the emitter expect a std::fmt::Write instead of an std::io::Write?

[carsonmyers]

It seems like it'd be useful to emit to an open file or socket, but it seems like fmt::Write is rather limited

[chyh1990]

Thanks. The emitter is designed for debug purpose in the first place. Yes, I think we should add support for io::Write.

[mkindahl]

Is there any interest in a PR for this? I see that there is a lot of outstanding PRs, so I wonder how active this repo is.