SimBDReverse distribution

SimBDReverse(Number lambda, Number mu, Taxa taxa, Number rho)

A complete birth-death tree with both extant and extinct species.
Conditioned on (a fraction of) extant taxa.

Number lambda - per-lineage birth rate.
Number mu - per-lineage death rate.
Taxa taxa - The extant taxa that this process are conditioned on
Number rho - The fraction of total extant species that the conditioned-on taxa represent. The resulting tree will have taxa.ntaxa()/rho total extant taxa.