Plot censored data.
Plot a graphical representation of censored data specified by a two-column matrix of left and right interval endpoints. The grid of potential knots used by
logcon is also shown.
a two-column matrix of left and right endpoints of data intervals.
the maximal distance between two consecutive grid points in the depiction of the grid used by
an optional vector of “spots” to be marked by ‘x’ for the intervals.
Used for the side effect.
## See the examples for logcon