Exercise to Book Chapter mapping

| Exercise | Book Chapter | |------------------------|--------------| | variables | §3.1 | | functions | §3.3 | | if | §3.5 | | move_semantics | §4.1 | | primitive_types | §4.3 | | structs | §5.1 | | enums | §6 | | modules | §7.2 | | collections | §8.1, §8.3 | | strings | §8.2 | | error_handling | §9 | | generics | §10 | | option | §10.1 | | traits | §10.2 | | tests | §11.1 | | standard_library_types | §13.2 | | threads | §16.1 | | macros | §19.6 | | clippy | n/a | | conversions | n/a |