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);
`

從 issue 中所示的 Parser.Default.ParseArguments 和 MapResult 進入點開始，然後追蹤說明文字的產生方式。當呼叫端能夠在每次執行時一致地包含應用程式標頭，或完全省略該標頭，且行為符合要求的選擇時，工作即告完成。

由索引模型根據 Issue 內容生成。