Saying that a type *implements* a trait is much more idiomatic than saying it *defines* the trait.

* Change "four eights" to "four u8s"
* Change "a 32" to "a u32"

 - Consume result of thread join()
 - Add link to threading model

Catch thread in example

Since this is an example, the code will be copied by many people and should be over correct.

?r @steveklabnik

Reword the short diagnostic for E0509

Saying that a type *implements* a trait is much more idiomatic than saying it *defines* the trait.

Preserve span when lowering ExprKind::Paren

Fix rust-lang#33681.

…=arielb1

[MIR] Add PointerCast for Unsize casts of fat pointers.

Fixes rust-lang#33387.

r? @eddyb

…Manishearth

Add new error code tests

r? @steveklabnik

Clarify wording in `transmute` example

* Change "four eights" to "four u8s"
* Change "a 32" to "a u32"