Add showHelpAfterError

[shadowspawn]

Pull Request

Problem

Some users would like the help displayed along with the error, or a tip that the help is available.

Related: #7 (comment) #482 #766 #919 #1423

Solution

Add .showHelpAfterError() to turn on displaying the help, and can optionally take a string to display (rather than the full help).

The form of the solution inspired in part by Yargs showHelpOnFail.

Example uses:

program.showHelpAfterError('(see --help for additional information)'); // custom suggestion

program.showHelpAfterError(); // display full command help after the error message

ChangeLog

• add: .showHelpAfterError() to display full help or a custom message after an error
• changed: remove help suggestion from "unknown command" error message (see .showHelpAfteError() )

[abetomo]

LGTM

[shadowspawn]

Thanks @abetomo