Given a set of predictive quantiles from a distribution, estimate the
distribution and create `d`

, `p`

, `q`

,
and `r`

functions to evaluate its density function,
distribution function, and quantile function, and generate random
samples. On the interior of the provided quantiles, an interpolation
method such as a monotonic cubic spline is used; the tails are
approximated by a location-scale family.