v0.2.1

• Added CowExt::to_slash and CowExt::to_slash_lossy. PathExt is no longer necessary to convert Cow<'a, Path> paths into slash paths.
• Clarified minimum supported Rust version. Rust 1.38 or later is supported. rust-version field in Cargo.toml was added so that cargo can check the MSRV is met.
• Improved documents of trait methods. The documents were moved from implementations of the trait methods to definitions of them so that users can find out the documents more easily. Documents for implementations are folded by default, but definitions aren't.