Allow for custom styling within prose

[samrobbins85]

When using something like MDX you might want to add custom components in your markdown, however their style is influenced by the prose styling and it is not easy to remove this.

A possible solution to this is to use the :not pseudo-class as demonstrated in this stackoverflow post

There is a possibility that some markdown processors will add classes to elements, so it might be best to have this as an option you can enable

[mathieutu]

duplicate of #32

[samrobbins85]

Oops, thanks for letting me know