Add categories for operating system APIs
Add categories for operating system APIs

steveklabnik/crates.io,Susurrus/crates.io,rust-lang/crates.io,Susurrus/crates.io,rust-lang/crates.io,Susurrus/crates.io,rust-lang/crates.io,steveklabnik/crates.io,rust-lang/crates.io,steveklabnik/crates.io,steveklabnik/crates.io,Susurrus/crates.io