o Lexis:
  - should accept variabels of class Date (and POSIXc / date / chron).
  - should not crash when one input record is completely
    outside range(breaks).
  - better specifcation of the included variabels in Lexis (either as
    variable numbers in the dataframe or as a character vector of the
    names, preferably both). Defaults to all variables in dataframe.

o stat.table:
  - change the digits option of the print method. When summing
    failures 0 digits is wanted, when summing person-years 1 is
    wanted.
  - more than one quantile permitted.
  - Labelling of statistics in multi-way tables.

o ci.lin: 
  - Allow a character vector in subset, taking the union of the
    thus defined subsets.
  - Confint intervals as an option (complementary to ctr.mat (and diff?)).
