Added splineless model

A reviewer requested that the type I error be assessed for the model
which does not have the spline. A new method, broadenrich_splineless
accomplishes this by calling test_gam_ratio_splineless which is exactly
the same as test_gam_ratio with only the spline deleted in the model.

There are corresponding logic changes in other functions. Wherever a
check for broadenrich occurs, broadenrich_splineless has been added as
well.