Add impls for Vec

[1tgr]

Delegating to the existing slice impls.

Without these impls we could just compare two vecs as slices, but:

• It requires the &v[..] or v.as_slice() syntax, on both sides of the comparison
• The vecs have to outlive the assert (assigned to variables), meaning no one-liners like assert_abs_diff_eq!(foo().as_slice() bar.as_slice())