Add function periods.base.
Improve variable names and comments.
Rework periods, formulas & legislations to support periods of several days or months or years.
Don't fail when computing a yearly column with a period truncated with column.start and/or column.end.
Add Holder.delete_arrays method
Improve display of numpy arrays in formulas log.
Add doctest to tests.
Add parameter is_period_invariant to function reference_input_variable.
Factorize code to generate a simulation from a scenario.
Improve logging of formulas (especially arrays).
Formula methods don't depend from quifam, ..., quimen & idfam, ..., idmen anymore.
Add parameters to reference_input_variable & reference_formula functions.
Add "clone" methods to duplicate a simulation (used by fsolve instead of recreating simulation from surveys).
Add Travis-CI configuration.
Use pip to install flake8 in Travis-CI.
New "tools" module containing functions empty_clone & stringify_array.
Rework the construction of columns using classes, functions and decorators.
Increase version number to 0.4.
Add DatedFormulaColumn (with dated_function decorator). Use instants instead of dates in DatedFormula.