New method get_or_new_holder.
Add missing parentheses.
Cleaning
Cleanup imports.
Remove X_AXES.
Remove Pandas dependency. Remove obsolete modules.
Rework scenarios API.
Improve formulas debugging and convert results of functions to column types.
Improve error logging.
Add mechanisms for formulas functions to reshape their tables.
Add steps infos to simulations and entities.
Rename "compute" function to "calculate". Function "compute" now returns a holder and function "calculate" returns an array.
Add debug option to simulations (to show arguments and results of formulas). Repair calls to "compute" functions.
Add method Holder.new_test_case_array.
Remove _option from functions parameters. Differentiate persons-specific entities.