Replace IRC channel with Gitter (#1069)
Replace IRC channel with Gitter (#1069)

The Mozilla IRC network is being shutdown, see
https://blog.rust-lang.org/2019/04/26/Mozilla-IRC-Sunset-and-the-Rust-Channel.html
and http://exple.tive.org/blarg/2019/04/26/synchronous-text.
carllerche/mio,carllerche/mio