Exercise to Book Chapter mapping

Exercise	Book Chapter
variables	§3.1
functions	§3.3
if	§3.5
primitive_types	§3.2, §4.3
vecs	§8.1
move_semantics	§4.1-2
structs	§5.1, §5.3
enums	§6, §19.3
strings	§8.2
modules	§7
hashmaps	§8.3
options	§10.1
error_handling	§9
generics	§10
traits	§10.2
lifetimes	§10.3
tests	§11.1
iterators	§13.2-4
smart_pointers	§15, §16.3
threads	§16.1-3
macros	§20.5
clippy	Appendix D
conversions	n/a