The points in the d marginal processes \(N_{1}\), \(N_{2}\) ,..., \(N_{d}\) of a vector
of point processes are plotted versus the time index.
If one of the arguments date and axispoints is NULL, default axis are used.
Otherwise, the values in axispoints are used as the points in the time index in which axis ticks
and labels, from date, are drawn.