Directly evaluate nth derivatives of some numpy and scipy univariate functions that operate elementwise.

This adds a couple of files, so I made this a separate branch that I'm trying to merge.  The idea is that this reorganization removes a bunch of junk that was cluttering your algorithms.py file.  The new module called "nthderiv" basically adds a new keyword argument 'n' to a bunch of numpy and scipy.special functions, where n specifies the nth derivative.

Some of these functions are used in my dumb forward mode and pullback implementations in algorithms.py.  Presumably these forward and pullback implementations could be rewritten more efficiently in the future, in a way that does not use the direct evaluation of the nth derivative of the numpy and scipy.special functions.