Rename sys header crates, add mman constants

Cargo.lock

Cargo.toml

src/lib.rs

src/netinet/in/Cargo.toml

src/netinet/in/src/lib.rs

src/sys_mman/Cargo.toml

src/sys_mman/build.rs

src/sys_mman/cbindgen.toml

src/sys_mman/src/lib.rs

src/sys_mman/src/linux.rs

src/sys_mman/src/redox.rs

src/sys_resource/Cargo.toml

src/sys_resource/build.rs

src/sys_resource/cbindgen.toml

src/sys_resource/src/lib.rs

src/sys_socket/Cargo.toml

src/sys_socket/build.rs

src/sys_socket/cbindgen.toml

src/sys_socket/src/lib.rs

src/sys_stat/Cargo.toml