Typo corrected and updated copyright years
Add ARC::get method and implements the function from it. Add an example showing a simple use of ARC.
auto merge of #6639 : osaut/rust/arc-clean, r=brson

* Add ARC::get method and implements the function from it.
* Add an example showing a simple use of ARC.

Update PR #6622 to avoid git noise.

I will remove the function get later.