* Added an extra header with definitions of parametric versions of some major STDLIB ADTs, for use in user specs. * Said parametric versions are also accepted in ?FORALLs. * Wrote parametric wrapper modules for said ADTs, which PropEr can use to produce symbolic instances. * Returned instances of STDLIB's major ADTs are now properly instance- checked during spec testing. * Auto-ADT now recurses into unions, nonempty improper and nonempty maybe improper lists when parsing API functions' return types.