---------------

*   *Preulude.Backprop* module added with lifted versions of several *Prelude*
    and base functions.
*   `liftOpX` family of operators now have a more logical ordering for type
    variables.  This change breaks backwards-compatibility.
*   `opIsoN` added to export list of *Numeric.Backprop*
*   `noGrad` and `noGrad1` added to *Numeric.Backprop.Op*, for functions with
    no defined gradient.

*Internal*

*   Completely decoupled the internal implementation from `Num`, which showed
    some performance benefits.