Prepare for 1.5.0 release

[KodrAus]

Changes since the last release

Includes:

• Update examples for 2018 edition #159
• Rustdoc is now passing "doctest" cfg and not "test" anymore #172
• [*.rs] rustfmt #175
• Correct a typo in inline_lazy.rs #177
• Add a mutex_map example #173
• test: VAR; remove unused braces #179
• Upgraded spin to 0.7 for better performance #182

[taiki-e]

Note that #172 increased MSRV to 1.40. See BurntSushi/termcolor#35 for more:

cfg(doctest) implemented in Rust 1.38 as an unstable feature, and stabilized in Rust 1.40. It compiles fine on Rust 1.37 and older, but fails on Rust 1.38 and 1.39, where this feature existed as an unstable feature.

[KodrAus]

Ah thanks for the heads up @taiki-e 🙇 In that case I'll bump this up to 1.5.0