Changes 0.6.1 to 0.7.0

o Function Icens() for estimation of rates from intervalcensored 
  follow-up data by Martyn Plummer added.

o Function epi.eff by Michael Hills is added. Estimates effects in
  various epidemiological study types.

Changes 0.6.0 to 0.6.1

o Coding errors in thoro dataset corrected. Only concerning dates and
  status for livercancer diagnosis.

o Lexis.lines now allows col.life, lwd.life, pch.fail, col.fail and
  cex.fail to have the same length as the data, i.e. to produce
  individualized lines and points. As Lexis.diagram calls Lexis.lines,
  this facility is also available through Lexis.diagram.

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 Eventually they will be superseded by new facilities in Lexis.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.
