Changes in Version 0.5.0
  
  o Improvements to ss.ci function: density line, normal qq-plot, warnings when
  normality test fails
  o Improvements to capability analysis functions (ss.stuty.ca, ss.cp, ss.cpk), 
  warnings and bug corrections
  o New function ss.cc.getc4 to compute constant c4 for the unbiased estimator of the 
  standard deviation.
  o New functions ss.cc.getd2 and ss.cc.getd3 to compute mean and variance of
  the relative range distribution (R/sigma)
  o New dataframes ss.data.pc, ss.data.pc.big and ss.data.pc.r
  o New dataframe ss.data.strings
  o Now ss.rr function uses the new functions ss.cc.getd2 and ss.cc.getd3 to
  calculate control limits.
  
