Custom renderer fails to respect no_styles option

**Bug report**

This pull request introduces two tests. It shows that a class that inherits from `Redcarpet::Render::HTML` will not respect the `no_styles` option.

The second test ensures that it does work with the regular `Redcarpet::Render::HTML` class since it seems like there wasn't one for it.

Note: I tried a couple other options and they did seem to work.

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This is a PR to show what seems to me like a bug. I haven't written C in years and I am very unfamiliar with writing C extensions for Ruby. Unfortunately I do not think I will be able to fix it myself, but hopefully this will help.