DOC: javadoc improvements: typos, incorrect links, package-info

[remkop]

Most modules other than the main picocli module do not have package-info.html file.

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Javadoc for CommandLine.Help.ColorScheme.Builder, the ansi(CommandLine.Help.Ansi ansi) setter method incorrectly says

Returns the Ansi setting

that should be

Sets the Ansi setting

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The CommandLine.Help.Ansi.Style.parse(String) javadoc says:

strings starting with "bg(" are delegated to bg(String), others are delegated to bg(String).

That should be

others are delegated to {@link #fg(String)}.

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