Version 0.20

• switch to one sty file per package
• use LaTeX's new hooks
• declare undeclared variables
• new exercise setup mechanism which clearly determines the difference between definition,
  usage, and printing of an exercise; this also solves the problem with added goals in the
  exercise body in a collection
• re-write collection mechanism:
  • changes the behaviour of \collectexercises but doesn't require external files any more and more importantly doesn't require inputting files several times for multiple collections
  • drop \collectexercisestype
  • new \(de)activatecollection
  • new options collect and <type>/collect
• small improvements in performance
• new parameters within and the-counter
• make no-files the default, new option use-files
• new examples
• various small fixes