This avoids the confusion between Zero() and IsZero() which sounds like they should be related
to one another but are not. This makes IsEmpty the counterpart to Reset. Add check for Zero in allMatrix
Fixes#1083.
Updates #1081.
* diff/fd: implement Hessian finite difference, and code cleanups.
This commit primarily adds the Hessian function for finding a finite difference approximation to the Hessian. At the same time, it combines duplicated functionality across the difference routines so that the preludes to all the difference routines look similar
