missing From<Vec<T>> for Cow<'a, [T]> impl

[talchas]

Both Vec and &[T] are missing From impls for Cow, unlike String/&str and PathBuf/&Path. Coherence is not (afaict) an issue, since the impl would be in the same crate as Cow.

Is there some reason these don't exist (do they cause coherence issues in downstream crates or something)?

[alexcrichton]

Whoa, I have no idea why these aren't implemented... Should be good to go ahead and add them! Want to send a PR?