[?][Design] Should %%assist return Markdown output?

[rgbkrk]

I'm starting to think that we should emit markdown output instead of creating a new cell with %%assist.

Reasons:

• Responses tend to come back in either Markdown or a plain text format
• set_next_input (the IPython new cell creator) can't stream updates
• The response usually needs some editing
• The document gets littered with new cells on repeated runs