Working version. To be removed the part concerning the vector of times.
This vector is intended to create statistics of the waiting times as
control to the coded simulator.
Changed Functions to a class in order to include a more consistent and
reliable random generator (ran.h).
Corrected all the bugs in order to be functional.
Added FunctionClass to include a new pseudo-random number generator.
Revisited also the computation of theoretical results in order to check
for cases with zero rates.