Remove mtimesDefault or move it to Data.Monoid

[Simon Jakobi]

Hi!

I was surprised to find two functions that appear to do the same thing
in Data.Semigroup:

  stimesMonoid :: (Integral b, Monoid a) => b -> a -> a       [1]
  mtimesDefault :: (Integral b, Monoid a) => b -> a -> a      [2]

Both are essentially versions of the default stimes implementation
that allow 0 as a multiplier.

I think it's confusing to have two functions with nearly the same
semantics but different implementations exported from the same module.

As stimesMonoid seems to fit well into the group of different stimes
implementations exported from Data.Semigroup, I propose that either

  1. mtimesDefault be deleted (after a suitable deprecation period)

or (particularly, if there still are plans to make mtimes a member of Monoid)

  2. mtimesDefault be moved to Data.Monoid (possibly with a deprecated
re-export from Data.Semigroup)

In case 2, I also think mtimesDefault should be made an alias of stimesMonoid.

Cheers,
Simon

[1] http://hackage.haskell.org/package/base-4.11.0.0/docs/Data-Semigroup.html#v:stimesMonoid
[2] http://hackage.haskell.org/package/base-4.11.0.0/docs/Data-Semigroup.html#v:mtimesDefault