MNT: Refactor constants (comments welcome)

closes #209 
This whole bit of parsing feels sketchy to me.  I would be in favor of usinng the tuples you get out of this function to generate a yaml file (named tuples have a `_to_dict` method which yields an ordereddict of the values).  It will be a bit bigger (as now the field names will be repeated everywhere) but will be more readable and parsable with standard tools.