Predprob updates 

This code does a two things. First, it completes the fix of the multinomial predictive probability issue, and second, it removes predictive_probability_density and changes the behavior of predictive_probability.

Predictive probability now returns the curve height rather than the probability over an interval. I have also removed the predictive_pdf functionality from the c++ code because it is no longer necessary since the math (s/2) discrepancy has been worked out. I have left the predictive_cdf function because there will be a point at which we will add probability over an interval functionality but that is on the back-burner at the moment.