Add HideHelp flag in App and Command
Hide "Options" sections in help, if no flags are defined
Fix Subcommand help text
Add Args.Swap command for swapping arguments

The usecase:
my-cli user <USERID> set <FIELD> <VALUE>

Being able to swap <USERID> with set argument, we can have nested subcommands while preserving all variable arguments along the way.
Add App and Command argument length checking
Add App.RunAndExitOnError shortcut