`Rc`

[Tamschi]

Is your feature request related to a problem? Please describe.

The current implementation is generic enough to support !Sync reference-counting for all consumers, too.

Describe the solution you'd like

Adapt sync::Arc into an rc::Rc struct.
The API should be extremely similar, but decrements and acquires should be relaxed.

Describe alternatives you've considered

None.

Additional context

There are opportunities for fallible (TryFrom) conversions between these types and Box.
Remember to .acquire() when moving away from either Arc or Rc!