Remove Markdown restrictions in some scopes

[Natrium729]

Themes: I believe all of them.

There are a lot of scopes that are Markdown-restricted and have no no-Markdown equivalent.

I'm thinking about entity.name.section.markdown and punctuation.definition.heading.markdown, among others. That's an issue since other languages that use these scopes won't have the headings highlighted. (It's the case for the Inform 7 extension I maintain, for instance.)

(And the same can be said for other scopes such as inline code, bold, italic and so on, of course.)