1. need to add a test for the akima splines2. [DOCUMENTATION] From: Conrad Curry <cwcurry@orca.st.usm.edu>  I would suggest adding more about cspline and Akima similiar to what  is given for 'polynomial', particularly under what conditions one  would be prefered over the other.3. add akima splines without the Wodicka modification, so that the splineis a smooth curve without corners.