Simulates punctuated trait evolution with punctuations that are rapid relative
to the spacing of samples. In practice, the time-series is divided into two or more
segments, each of which has its own mean and variance.
Segments are separated by punctuations. Population means in the ith segment are
drawn randomly from a normal distribution with a mean equal to ith element of theta
and variance equal to the ith element of omega. The magnitudes of punctuations are
determined by the differences in adjacent theta values.