Fix annotation mechanism in Pyccel parser:
Fix annotation mechanism in Pyccel parser:

  - Do not replace existing semantic parser (hence avoid processing same
    file twice);
  - Make sure that list of parents is always complete (leaf in parser tree
    can now have multiple parents);
  - Change function name: 'annotate_parents' >> 'annotate_sons'.

ratnania/pyccel,ratnania/pyccel