Changed ICgen settings to have decsriptions.
Changed ICgen settings to have decsriptions.

This is a significant change to how ICgen_settings.settings work.  Default
settings are now defined in the class definition as a list of length-3
tuples containing ('variable_name', default_val, 'description of variable').
This allows us to keep track of and see what all these settings mean by
calling settings.print_defaults()

ibackus/diskpy,ibackus/diskpy