Update to 1.31.0

Changelog:
Version 1.31.0 (2018-12-06)
Language

    This version marks the release of the 2018 edition of Rust.
    New lifetime elision rules now allow for eliding lifetimes in functions and impl headers. E.g. impl<'a> Reader for BufReader<'a> {} can now be impl Reader for BufReader<'_> {}. Lifetimes are still required to be defined in structs.
    You can now define and use const functions. These are currently a strict minimal subset of the const fn RFC. Refer to the language reference for what exactly is available.
    You can now use tool lints, which allow you to scope lints from external tools using attributes. E.g. #[allow(clippy::filter_map)].
    #[no_mangle] and #[export_name] attributes can now be located anywhere in a crate, not just in exported functions.
    You can now use parentheses in pattern matches.

Compiler

    Updated musl to 1.1.20

Libraries

    You can now convert num::NonZero* types to their raw equivalvents using the From trait. E.g. u8 now implements From<NonZeroU8>.
    You can now convert a &Option<T> into Option<&T> and &mut Option<T> into Option<&mut T> using the From trait.
    You can now multiply (*) a time::Duration by a u32.

Stabilized APIs

    slice::align_to
    sl

    ice::align_to_mut
    slice::chunks_exact
    slice::chunks_exact_mut
    slice::rchunks
    slice::rchunks_mut
    slice::rchunks_exact
    slice::rchunks_exact_mut
    Option::replace

Cargo

    Cargo will now download crates in parallel using HTTP/2.
    You can now rename packages in your Cargo.toml We have a guide on how to use the package key in your dependencies.


(ryoon)