Merge branch 'switch05-06' into 'main'

.gitlab-ci.yml

README.md

book/book.toml

book/src/SUMMARY.md

book/src/part05.md

book/src/part06.md

codes/rust_lang/part00/src/main.rs

codes/rust_lang/part05/src/io.rs

codes/rust_lang/part05/src/lib.rs

codes/rust_lang/part05/src/main.rs

codes/rust_lang/part05/src/minimum.rs

codes/rust_lang/part05/src/something_or_nothing.rs

codes/rust_lang/part06/src/io.rs

codes/rust_lang/part06/src/lib.rs

codes/rust_lang/part06/src/main.rs

codes/rust_lang/part06/src/main_old.rs

codes/rust_lang/part06/src/minimum.rs

codes/rust_lang/part06/src/something_or_nothing.rs