Changes in Version 8.1-0

  o New package pwt8 for PWT 8.1 (originally released in
    April 2015). It is an updated version of PWT 8.0,
    covering the same countries and period.


Changes in Version 8.0-0

  o New package pwt8 for PWT 8.x. So far only PWT 8.0 has
    been released (in July 2013) and has been added as
    pwt8.0.
