Large reorganization of headers (WIP)

Cargo.lock

Cargo.toml

Makefile

build.rs

header.sh

src/arpainet/Cargo.toml

src/arpainet/build.rs

src/crt0/Cargo.toml

src/crt0/src/lib.rs

src/ctype/Cargo.toml

src/ctype/build.rs

src/dirent/Cargo.toml

src/dirent/build.rs

src/errno/Cargo.toml

src/errno/build.rs

src/fcntl/Cargo.toml

src/fcntl/build.rs

src/fenv/Cargo.toml

src/fenv/build.rs

src/float/Cargo.toml