Add support for periods.
ALlow formulas to specify the period of the legislation parameters they use.
Add flake8 config
Remove H* errors
Add period to JSON of scenarios.
Sort method fill_simulation and removes its return value.
Factorize method of scenarios that sets the axes of the simulation.
Factorize method of scenarios that sets the variables of a simulation.
Add support for multiple periods in JSON of input variables and axes.
Factorize conversion of JSON or Python to axes.