Delete send_str, rewrite clients on top of MaybeOwned<'static>
Delete send_str, rewrite clients on top of MaybeOwned<'static>

Declare a `type SendStr = MaybeOwned<'static>` to ease readibility of
types that needed the old SendStr behavior.

Implement all the traits for MaybeOwned that SendStr used to implement.

rust-lang/rust.vim