Improve compatibility of supernote with markdown

[codygunton]

Have you read the Longevity Statement?
Yes

Is your feature request related to a problem? Please describe.
Supernotes should be compatible with basic markdown in the sense that you can paste markdown in and it will be correctly interpreted.

Describe the solution you'd like
When I paste a markdown file into an existing super note, it should "just work", at least for basic markdown. For instance, the engine should recognize headlines and convert them. At the moment even converting by hand is extremely inconvenient--somehow everything either ends up headline format or headlines end up in normal text form.

Describe alternatives you've considered
Just use the markdown format. But most of what I write is potentially something I want to share with someone, do I just default to markdown? How will I know when I'm safe to use super?

Additional context
None to offer.

[sanzot]

+1