Impl `Clone` for `EcoVec::IntoIter`

[molarmanful]

Hi, was wondering whether it would be possible to make EcoVec::IntoIter Clone, or if there is some hidden gotcha I'm missing. My current workaround is to do:

vec.to_vec().into_iter()

Thanks in advance!

[laurmaedje]

A naive impl should be fairly simple. A more efficient impl that makes use of the reference counting, I'm not so sure.

[laurmaedje]

I've decided that I'd rather not support this in ecow, as there does not seem to be a perfect solution and I'd rather keep the trade-offs explicit. See #57 for more details.