Remove `use` in `match`. Should be as own RFC, and not willing to defend it personally.
Likewise, removed parts in the how we teach and drawbacks, making those sections less
"if"fy.

Added `trait`, as that's analogous to `impl` and I feel stupid for not doing that initially.

Added grammar changes. Not sure if they're the right changes, but at least they exist.

There's RFCs for having `pub use` in traits work as aliases, and
allowing `pub use` would be a back-compat hazard for these RFCs.

Sorry trait authors.