Update mio dependency

[asafigan]

mio version 0.6 depends on deprecated crate. Upgrade to version 0.7.

[hannobraun]

Thanks for the the note!

[ids1024]

And likewise, tokio 0.3, which has recently been released.

Updating both seems mostly easy, except for the fact Tokio no longer includes PollEvented in its public API (it no longer exposes it's dependency on mio in the public API in general).

I suppose the solution would be to manually implement AsyncRead and AsyncWrite similarly to how PollEvented does it?

[hannobraun]

Thanks, @ids1024. Any pull requests doing such upgrades are definitely welcome. Not sure what the best way to handle PollEvented would be. I still don't have significant experience with the whole async ecosystem (that work has always been driven by contributors).

[ids1024]

I think this could use AsyncFd which was just merged into tokio. So I guess this is waiting on the next minor Tokio release.