Add survival probability function to continuous distributions

It is useful to know the survival function of a number given a continuous distribution.

While this can be approximated with

1 - cdf(x)

, there is an opportunity for greater accuracy in certain distributions.

A good example of this is the gamma distribution. The survival function for that distribution would probably look similar to:

@Override
 public double survivalProbability(double x) {
     if (x <= SUPPORT_LO) {
         return 1;
     } else if (x >= SUPPORT_HI) {
         return 0;
     }
     return RegularizedGamma.Q.value(shape, x / scale);
}