feat(pddlpy) Add support for durative-actions
feat(pddlpy) Add support for durative-actions

This commit rewrites many parts of pddl.py. The changes are probably not
backward compatible. For this, the following features are added:

* No more distinguish between precondition_pos and *_neg, but new class
  Goal that allows to nest Goal with all possible operators: and, or,
  not, imply, exits, ...

* Similar for effect: New class Effect with operators: and, not, when,
  forall, ...

* Support for durative-action:
  * with goal operators at start, at end, over all
  * with effect operators at start, at end
  * support for durations

hfoffani/pddl-lib