• cut out exporter-related cruft; it was only necessary when needing
  to choose between multiple implementations (Toby Inkster)
  
• Reorganize and clarify documentation (David Golden)
  
• revise SYNOPSIS and DESCRIPTION for revised export model (David
  Golden)
  
• introduce ":like_*" import tags (Toby Inkster, Jens Rehsack)
  
• remove Data::Tumbler and Module::Pluggable from configure
  dependencies, they're coming with Test::WriteVariants