Add default argument to prestations.
Remove Prestion (replaced by Column).
Finish removing Prestation
Create real columns for birth and prenom.
Rename AgesCol to AgeCol.
Remove Column.legislative_input boolean: It is not used.
Remove "Abstract" from formula names.
Rename Formula calculate to function & __call__ to calculate.
Remove useless initialization.
Remove commented code.
In columns, rename _default to default, _dtype to dtype & _func to function.
Add AlternativeFormula (for age & agem).
Improve columns JSON.
FC