[ refactor ] Add Data.Nat.SumAndProduct

[jamesmckinna]

Implements the 'provisional' v2.3 fix for #2553 .

NB.:

• starting from a blank CHANGELOG in anticipation of Update documentation from v2.2 release version to v2.3-dev #2557 being merged
• fixes a spurious deprecation message from v2.0 in Data.List.Properties concerning sum-++-commute, but now the message is... anachronistic. Wasn't sure how to deal with this properly!
• can't seem to understand why the deprecation warning is issued when checking Data.Nat.Primality.Factorisation when generating the HTML index, but not when testing stdlib! Nor why it is being generated... but I may have forgotten the fine(r) points about how this works... :-( UPDATED: seemingly FIXED now!?

[Taneb]

I have to say, I don't like the module name... there are other monoids on Nat (e.g. (max, 0)) whose folds we'd also want to have in the same module if we have them.

[jamesmckinna]

Thanks @Taneb !

Bear in mind that I regard this PR as provisional, indeed minimal wrt not refactoring to lift out the actual Monoid abstractions as such, before a 'proper' (breaking) refactoring which will deprecate/remove this module, and all traces of the original definitions. In particular, I would want this PR only to emulate existing functionality (but product-++ seemed too tempting not to add, emphasising the need to abstract the constructions...?), rather than try to generalise it to arbitrary monoid structures arising on Nat. Perhaps that's a failure of imagination/nerve?

Eg, I could even imagine doing that generalisation (in whatever form) downstream, and then simply deprecating this module with its 'clunky' name. perhaps I even thought that would be inevitable, so either didn't care, or actively chose, to make the name 'clunky'... on a 'build one to throw away' principle...

That said, would (any of) the following be better candidate names?

• Data.Nat.MonoidAction/Data.Nat.FreeMonoidAction (a bit too general, since we're only considering the action of Nat on itself...?); it's a pity I haven't/hadn't managed to finish Add Algebra.Action.* and friends #2350 before this, but I've been trying to not let the 'perfect design' get in the way of progress... ;-), but eventually, as with Refactor Data.Nat.GeneralisedArithmetic #2446 , there ought to be a grand refactoring of all this stuff...
• Data.Nat.Monoid

Other suggestions welcome! @JacquesCarette any thoughts on this?

[JacquesCarette]

As I said elsewhere, fully agree with moving these out of where they currently are.

Hmm, why Data.Nat.* though? I was thinking of these as "special cases of List-based computation" and so under Data.List. Data.List.NatActions? [Obviously not wedded to that awkward name, but pushing things along.]

If it were in Data.Nat then I'd see it being way more general, i.e. over any foldable container.