Officially deprecate Saturating

[benluelo]

The Saturating trait was deprecated here: 86c3126, but not officially (i.e. no #[deprecated, reason = "..."] attribute). Is there a reason for this? Would it be possible to do this?

[benluelo]

Possibly related to #47, although I don't think that deprecating a trait is a breaking change

[cuviper]

It's unfortunately tied to the PrimInt trait, as mentioned in #165 (comment). For that reason, I think a "soft" deprecation is better so folks don't have to squash a warning they can't otherwise avoid. There's also no inherent disadvantage to using Saturating -- it's just not consistent with how we did Checked* and Wrapping* traits.

Deprecation is not a breaking change though, you're right about that.