Implement mtime and atime copying

[pczarn]

No description provided.

[schneems]

FWIW I need exactly this feature to solve heroku/buildpacks-ruby#302 (comment). I found another crate https://crates.io/crates/cp_r, however that crate is missing options I need (like the ability to overwrite an existing file) that fs_extra has.

I see this was opened nearly 3 years ago and there's been no comment. I'm unsure if it got reviewed and rejected without a comment (by accident, it happens) or if perhaps it got lost in the shuffle and would be accepted either in its current state or with some changes.

[pczarn]

@schneems This feature should work. The test for this passes, even if other tests in the project seem not to pass. I would probably mark the PR as WIP if it did not work.

[pczarn]

@schneems the author of the project is busy with paid work, which is why there was no comment