Document and expose Ordering when backed by an Atomic

[smalis-msft]

The documentation should mention that current methods (like get and set_aliased) when called on a type with an AtomicFoo backing will used Relaxed orderings. It would also be nice if methods were exposed that allowed specifying custom orderings for these operations.

[hechang27-sprt]

Yep, I find it weird that despite seemingly supporting atomic integer, there is not a single example in the documentation about it.