Move crt0 and platform into src folder

Cargo.toml

fmt.sh

src/crt0/Cargo.toml

src/crt0/src/lib.rs

src/ctype/Cargo.toml

src/fcntl/Cargo.toml

src/grp/Cargo.toml

src/mman/Cargo.toml

src/platform/Cargo.toml

src/platform/src/lib.rs

src/platform/src/linux/mod.rs

src/platform/src/rawfile.rs

src/platform/src/redox/mod.rs

src/platform/src/types.rs

src/semaphore/Cargo.toml

src/stdio/Cargo.toml

src/stdlib/Cargo.toml

src/string/Cargo.toml

src/template/Cargo.toml

src/unistd/Cargo.toml