Display help without requiring ParseArguments

**Issue by [Steve887](https://github.com/Steve887)**
_Wednesday Jan 20, 2016 at 01:30 GMT_
_Originally opened as https://github.com/gsscoder/commandline/issues/281_

----

I'm trying to print the help text for my options without having to force a parser error.

Currently, it seems the only way to print the help text is to call something like

```
Parser.Default.ParseArguments(new string[] { "verb", "--help" });
```

I see there's `HelpText.AutoBuild` but that seems to require a NotParsed result.

Is there a way to write the help text for an options class without having to parse arguments? Maybe something like `HelpText.DisplayHelp`?

Start by reading Parser.Default.ParseArguments and HelpText.AutoBuild, using the Options class and the existing --help example as the entry points. Determine how help text can be generated without forcing a NotParsed result, then verify that the resulting output matches the help produced through parsing.

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