Version 0.11
    o Fixed w_table(), an internal object was inadvertently returned.
    o Improved printing of crosstables

Version 0.10
    o New functions w_mean(), w_var() and w_sd(), w_quantile and w_median, to 
      obtain weighted versions of mean, variance and standard deviation,
      quantiles and median, respectively, adapted to declared objects
    o Fixed a bug in as_haven.declared(), when all values are (declared) missing
      and labels are not numeric
    o Argument "weight" changed to "wt" in w_table()
    o New arguments in function w_table(): "observed" to only print observed
      values, and "margin" to calculate proportions in crosstabs
    o Function w_table() now accepts a second argument "y" to create crosstabs
    o Function frtable() renamed to w_table() standing for weighted table

Version 0.9
    o New argument "weight" in function frtable(), allowing to weight not only
      valid but also missing values
    o More robust function frtable() in treating declared values with
      overlapping labels (e.g. hierarchical ISCO codes and categories)
    o Fixed a bug in declared() when all values are completely missing

Version 0.8
    o Improved treatment of equality and non-equality, now accepting labels as
      well as values
    o Reverted functionality to not dropping the attributes in arithmetic
      operations, this is now left to the users' preference

Version 0.7
    o Bug fix saving declared data frames as .csv files
    o as_declared() now retains the "format.spss" attribute, if existing

Version 0.6
    o Improved treatment of arithmetic operations, attributes are no longer
      propagated (thanks to Randall Pruim for the suggestion)
    o Modified as_haven() for objects of class 'declared', to avoid a bug in
      package ReadStat that prevents exporting missing values to SPSS for
      integer variables

Version 0.5
    o Initial version
