Changes in Version 0.2-0

  o zoo() now has defaults for both arguments x and order.by,
    which mimic the default behaviour of ts().

  o added new aggregate.zoo() method for computing summary
    statistics of "zoo" objects along a coarser index grid.

  o improved merge.zoo() in three directions:
    1. handling of "zoo" objects with zero columns,
    2. naming of columns in the merged "zoo" object
       which behaves more like merge.data.frame();
       a corresponding suffixes argument has also been added,
    3. introced a fill argument which allows to fill gaps
       by another value than NA.
       
  o improved documentation with extended examples
