dplyr package has been moved from Depends to Imports field;
package argument has been added to the function qsurv() to ensure that the right function from the right package is found depending on the search path;
Function inv_pgf() was reimplemented to allow the use of the stats::poisson() function in the the incidence argument.
the r*reg() functions now make sure that there is always a baseline distribution, like in the function survival::coxph().
