Add HideHelp flag in App and Command
Hide "Options" sections in help, if no flags are defined
Fix Subcommand help text
Fix tests
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.RunAndExitOnError shortcut
Add App and Command argument count checking
Merge remote-tracking branch 'origin/hidehelp'
Merge remote-tracking branch 'origin/shortcut'
Merge remote-tracking branch 'origin/args'