Extend .argument() to add default value and custom parse for command-argument

[shadowspawn]

Pull Request

Problem

Follow through with the idea that .argument() follow same pattern as .option(), with support for default value (for optional arguments) and custom command-argument parsing.

Solution

Support for default value (for optional arguments) and custom command-argument parsing.

Implementation notes:

• not emitting events for the arguments
• only processing the arguments for the action handler, not for program.args
• custom processing for arguments uses same style function as for options

ChangeLog

• add default value for optional command-arguments
• add custom processing function for command-arguments
• deprecate InvalidOptionArgumentError (replaced by InvalidArgumentError)
• CommanderError code commander.invalidOptionArgument renamed commander.invalidArgument

[abetomo]

extraInfo appears to have only 0 or 1 elements.
Does it need to be an array?

[shadowspawn]

Fair question. No, does not need to be an array currently. However, I left in the array as planning to add choices, like optionDescription which I copied the code from.

[abetomo]

LGTM!

[shadowspawn]

Thanks @abetomo