Control over Help Text Headers

When (and only when) the help text is shown, it adds the application name, version, and copyright info before writing the options details. However, I'd either like to include with every run, or exclude it completely so I can output my own info. However, I can't figure out how to do that.

I'm just using the default ParseArguments/MapResult code:

`
return Parser.Default.ParseArguments(args)
.MapResult(
(AddOptions opts) => RunAddAndReturnExitCode(opts),
(CommitOptions opts) => RunCommitAndReturnExitCode(opts),
(CloneOptions opts) => RunCloneAndReturnExitCode(opts),
errs => 1);
`

从 issue 中所示的 Parser.Default.ParseArguments 和 MapResult 入口点开始，然后追踪帮助文本的生成方式。当调用方能够在每次运行时始终包含应用程序标头，或完全省略该标头，并且行为与请求的选择一致时，工作即告完成。

由索引模型根据 Issue 内容生成。