v0.4.0

What's new:

• Added Yazap.displayHelp and Yazap.displaySubcommandHelp to manually display root command help and provided subcommand help respectively
• Added Command.addArgs and Command.addSubcommands

Breaking changes:

• Command.takesValue, Command.argRequired, Command.subcommandRequired,
  Arg.takesValue, Arg.takesMultipleValues and Arg.allowedEmptyValue is removed and now you have to use applySetting and removeSetting to set and unset setting
  Ex:

  var app = Yazap.init(allocator, "app", null);
  defer app.deinit();
  
  var cmd = app.rootCommand();
  cmd.applySetting(.takes_value);

Fixes:

• Fixed v0.10.0 optional specifier error messaged (#6)
• Now parsing will be stop after encountering help option (-h or --help)