Changes from 0.4 to 0.6

o ci.pd() amended to support the Agresti-Caffo method for confidence
  intervals for difference between proportions. Newcombes method 10
  is still used in twoby2.

o apc.fit() added. Fits age-period-cohort models with a range of
  possibilities for parametrizations.

o Functions for time-splitting at arbitrary times and at recurrent 
  failures have been added: isec(), icut(), fcut1(), fcut() and
  ex1(). Eventually they will be superseded by new facilities in Lexis.

o Function apc.plot() to make a plot of an apc fit is added. It is just
  a wrapper for apc.frame() and apc.lines(), with suitable computation of
  the paramters supplied to apc.frame.

o Lexis.lines(): pch.fail and col.fail expandS to vectors of length two
  if only one value is given. 

o ci.cum() aimed at computing cumulative hazard functions from
  parametric functions for hazards.

o Problem in print.floated() with printing of objects of class
  "floated" fixed.

o Problem in ci.lin when subset did not match any factor names and
  diff=T was given the function crashed. Fixed, and documentation updated.

o cal.yr produces objects of class c("cal.yr","numeric"). Functions
  as.Date.numeric and as.Date.cal.yr added.
