raise an error (the correct value was still computed though)

explicitly unit tested

Ready to merge: Adds a unit test of undefined gradients on integers

Ready to merge: remove g_cost

Added MonitorMode as a debugging tool

Fixed indentation.

Fixed a few typos.  See library/printing.html.

Fixed a typo.

Fixes several issues with gradients and some other bugs

rather than having an error

was iterable

wrt