Significant refactoring (by Kent Fredric++) to make the filters pluggable.

• Fixes RT#85076 bug (support for returns() syntax)
  
• Switches to named captures to make the regex more clear (ok, since we
  already require 5.010 for the balanced paranes)
  
• Stores signature (and any returns() declaration) externally rather
  than in the code via comments. Nice idea Kent++.
  
• Adds a .perltidyrc file so all contributers style will be consistent