HelpProvider colors should be configurable

[FrankRay78]

fixes #1379

• I have read the Contribution Guidelines
• I have commented on the issue above and discussed the intended changes
• A maintainer has signed off on the changes and the issue was assigned to me
• All newly added code is adequately covered by tests
• All existing tests are still running without errors
• The documentation was modified to reflect the changes OR no documentation changes are required.

Changes

• Ability to configure the styling used by the HelpProvider, eg

configurator.Settings.HelpProviderStyles = HelpProviderStyle.BoldHeadings;

HelpProviderStyle offers three styling options OOTB, Default, BoldHeadings, None

None offers maximum accessibility.

The examples project was updated accordingly, eg:

namespace Help;

public static class Program
{
    public static int Main(string[] args)
    {
        var app = new CommandApp<DefaultCommand>();

        app.Configure(config =>
        {
            // Register the custom help provider
            config.SetHelpProvider(new CustomHelpProvider(config.Settings));

            // Render an unstyled help text for maximum accessibility
            config.Settings.HelpProviderStyles = HelpProviderStyle.None;
        });

        return app.Run(args);
    }
}

Spectre.console users can set whatever colours they wish, in a similar way the HelpProviderStyle factory does below:

            HelpProviderStyle styles = default(HelpProviderStyle);

            styles.Description.Header.Markup = "yellow";
            styles.Usage.Header.Markup = "yellow";
            styles.Usage.CurrentCommand.Markup = "underline";
            styles.Usage.Command.Markup = "aqua";
            styles.Usage.Options.Markup = "grey";
            styles.Usage.RequiredArgument.Markup = "aqua";
            styles.Usage.OptionalArgument.Markup = "silver";

[FrankRay78]

Major refactoring has now been done to address all review comments @patriksvensson, including a rewrite of the accompanying documentation. It's also now a PR I can be proud of. Happy to address any further issues stopping this from being merged.

[FrankRay78]

Further refactoring done, good review comments @patriksvensson.

[patriksvensson]

Merged! Thank you for your contribution. Much appreciated! 👍