Rust 1.39.0 released

Version1.39.0 of the Rust language is available. The biggest new featureappears to be the async/await mechanism, which is described in thisblog post: "So, what is async await? Async-await is a way towrite functions that can 'pause', return control to the runtime, and thenpick up from where they left off. Typically those pauses are to wait forI/O, but there can be any number of uses."