Allow one to programatically trigger the help screen

[bramus]

An extra (public) function showHelp() which triggers writeHelp() (with its proper arguments) would be nice to have.

[dpiquet]

I would also find it useful !

In fact i already changed Cli::writeHelp function from private to public so i can call it from my own code. Seems no other changes is required to make it work. I just have to load the appropriate schema using Cli::getSchema (which was already public) so i can give it back to the writeHelp function.

[bramus]

Awesome, thanks!