Fix misspelled comments.
Use cargo new.

Now that this feature exists, we should use it.

Fixes #16078
Add note about Cargo.lock
Fix manual regarding attribute placement.

Fixes #15494.
auto merge of #16180 : jbcrail/rust/fix-comments, r=steveklabnik
auto merge of #16186 : steveklabnik/rust/guide_cargo_new, r=alexcrichton

Two commits here: one to add `cargo new` to the guide, and a second to mention the lockfile that Cargo now generates.
auto merge of #16189 : steveklabnik/rust/gh15494, r=alexcrichton

Fixes #15494.
Fix misspelled comments for tests.