parseArgs

Parses command-line arguments using an immediate callback surface.

The parser calls body once for each argument. The callback should call mode and match methods on the provided ArgStep to declare and match the current argument. After input is exhausted, the parser calls the callback one final time with step.complete set so required options and operands can be validated from the same declarations.

config may be null, in which case the parser uses AUTO syntax, automatic help, standard output for help, and standard error for diagnostics.