Query:
- evaluate():
  - left and skip are no-longer clusure variables, greatly simplifying edge cases
  - i is no longer a parameter, always initialized to zero at the start of evaluate()
  - "failed" operator: set skip value
  - always skip even when operator "accepts_fail"
  - improve/simplify operator parameters evaluation
- evaluate_object() now inner function of evaluate(), removes repeated code
- Operator option "do_not_evaluate_parameters" allows to retrieve litteral Array values
- Add 16 tests