`text_markup: Literal["rich", "markdown", "rst", None]` config option

[dwreeves]

• Add text_markup: Literal["rich", "markdown", "rst", None].
• Add optional rich-click[rst] support via the rich-rst package. https://github.com/wasi-master/rich-rst Very small package, but seems fine, so an optional dependency would work.
• Silently deprecate/discourage use_markdown: bool and use_rich_markup: bool.
  • I don't not think it is worth warning.warn()ing users about this one. This is the sort of thing I'd deprecate only on release of a rich-click==2.0.0. It's just too trivial to support the bool args, and I would feel bad warning polluting users' warnings with this one.
  • However, I do think we should start to warn users via UserWarning when there are conflicts in in the config, since only one can be supported at a time.

    enabled_markup_options = sum(map(bool, [self.use_rich_markup, self.use_markdown, self.use_rst]))
    if enabled_markup_options > 1:
      import warnings
      warnings.warn(...)
    if enabled_markup_options == 1 and self.text_markup is not None:
      import warnings
      warnings.warn(...)

[dwreeves]

Oh no, this can't go out for 1.8. The rich-rst library has some issues that make it not play nicely with what we're doing. I will have to reach out to the owner of this library separately and see what we can do.