Implement Clone for IntoIter where A: Clone

[L0uisc]

Implements Clone for IntoIter<A> where A: Array + Clone and A::Item: Copy (necessary to be able to use from_slice()) as per #178.

I also left a commented implementation which requires A::Item to be the more relaxed Clone, which also works. However, it will be less efficient than the other impl when the types are Copy because it can't use from_slice(). I believe the feature I'm looking for is specialization?

[mbrubeck]

Ah, I forgot that from_slice requires Copy.

I think we should use the more-general, less-performant version for now, and when specialization is available we can use it to optimize the Copy case.

If you use SmallVec::from(slice) instead of SmallVec::from_slice(slice) then this should work for Clone types, and when the "specialization" Cargo feature is enabled it will use from_slice when possible.

[L0uisc]

Sorry, I'm trying out Visual Studio's git plugin, and it seems I'm doing things wrong...

[L0uisc]

#192 should be correct.