deepclone 0.3.1

Deep clone that copies shared data once: an `Rc`/`Arc` reached twice becomes one new `Rc`/`Arc`
Documentation 
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error: unknown `deepclone` field attribute, expected `clone`, `default`, or `with`
 --> tests/ui/unknown_field_attribute.rs:5:17
  |
5 |     #[deepclone(shallow)]
  |                 ^^^^^^^