* Added `ABP` newtype wrapper to *Numeric.Backprop.Class* (re-exported from
*Numeric.Backprop* and *Numeric.Backprop.Explicit*) to give free `Backprop`
instances for Applicative actions.
* Added `NumBP` newtype wrapper to *Numeric.Backprop.Class* (re-exported in
the same places as `ABP`) to give free `Backprop` instances for `Num`
instances.
* Added `^^?!` (unsafe access) to *Numeric.Backprop* and
*Numeric.Backprop.Num*.
* `Backprop` instance for `Natural` from *Numeric.Natural*. Should actually
be safe, unlike its `Num` instance!
* `zfFunctor` and `ofFunctor` for instances of `Functor` for
*Numeric.Backprop.Explicit*.
* `realToFrac` and `fromIntegral` to *Prelude* modules
* `T2` and `T3` patterns for *Numeric.Backprop*, for conveniently
constructing and deconstructing tuples.