Functions implementing the Bernoulli-Weibull distribution, in which zero values
occur with probability 1-prob and non-zero values follow a Weibull
distribution with scale and shape parameters.
dbweibull gives a probability density function (pdf),
pbweibull gives the cumulative distribution
function (cdf), qbweibull gives the quantile function (inverse cdf),
and rbweibull is used for generating random variates.