Remove simulation drawing methods from core and convert them to functions.
Move TaxBenefitSystem class to its own module.
Remove duplicate code.
Rename method handle_output_xml to generate_output_tree.
Sort methods by alphabetical order.
Improve some of the dangerous "except:" constructs.
Optimize generation of an OutNode repr.
Simplify OutNode iteration.
Slightly improve code grammar.
Optimize method OutNode.partiallychecked.
Slightly cleanup OutNode.
Improve repr of OutNode.
Add to_json method to OutNode.
Improve variable name.