To update, run rustup update stable.

• rustc avoids unnecessary memory copies in certain situations -> 5-10% less memory usage
• CommonMark for rustdoc
• http://doc.crates.io -> https://doc.rust-lang.org/cargo
• std::ascii::AsciiExt is deprecated because methods of the trait are directly defined for u8, char, [u8], and str
• Atomic types implement ::From their non-atomic types, e.g.: let x = AtomicBool::From(true)
• () now implements FromIterator<()>
• RwLock has had its Send restriction lifted
• cargo check can check your unit tests
• cargo uninstall can now uninstall more than one package in one command

https://blog.rust-lang.org/2018/01/04/Rust-1.23.html